doc: Documentation in Markdown for Depends Dir

Documentation more readable when viewed on Github.

Some extra changes by @laanwj:

- Make README.usage the default README. This is more convenient from a
  user perspective. Link to other documentation in this default README

- Add list of popular targets for cross compilation, change default to
  Win64 instead of Win32

1 files changed, 0 insertions, 130 deletions

diff --git a/depends/README.packages b/depends/README.packages
deleted file mode 100644
index 6d87402ebc..0000000000
--- a/depends/README.packages
+++ /dev/null
@@ -1,130 +0,0 @@
-Each recipe consists of 3 main parts: defining identifiers, setting build
-variables, and defining build commands.
-
-The package "mylib" will be used here as an example
-
-General tips:
-mylib_foo is written as $(package)_foo in order to make recipes more similar.
-
-Identifiers:
-Each package is required to define at least these variables:
-  $(package)_version:
-    Version of the upstream library or program. If there is no version, a
-    placeholder such as 1.0 can be used.
-  $(package)_download_path:
-    Location of the upstream source, without the file-name. Usually http or
-    ftp.
-  $(package)_file_name:
-    The upstream source filename available at the download path.
-  $(package)_sha256_hash:
-    The sha256 hash of the upstream file
-
-These variables are optional:
-  $(package)_build_subdir:
-    cd to this dir before running configure/build/stage commands.
-  $(package)_download_file:
-    The file-name of the upstream source if it differs from how it should be
-    stored locally. This can be used to avoid storing file-names with strange
-    characters.
-  $(package)_dependencies:
-    Names of any other packages that this one depends on.
-  $(package)_patches:
-    Filenames of any patches needed to build the package
-  $(package)_extra_sources:
-    Any extra files that will be fetched via $(package)_fetch_cmds. These are
-    specified so that they can be fetched and verified via 'make download'.
-
-Build Variables:
-After defining the main identifiers, build variables may be added or customized
-before running the build commands. They should be added to a function called
-$(package)_set_vars. For example:
-
-define $(package)_set_vars
-...
-endef
-
-Most variables can be prefixed with the host, architecture, or both, to make
-the modifications specific to that case. For example:
-
-  Universal:         $(package)_cc=gcc
-  Linux only:        $(package)_linux_cc=gcc
-  x86_64 only:       $(package)_x86_64_cc = gcc
-  x86_64 linux only: $(package)_x86_64_linux_cc = gcc
-
-These variables may be set to override or append their default values.
-  $(package)_cc
-  $(package)_cxx
-  $(package)_objc
-  $(package)_objcxx
-  $(package)_ar
-  $(package)_ranlib
-  $(package)_libtool
-  $(package)_nm
-  $(package)_cflags
-  $(package)_cxxflags
-  $(package)_ldflags
-  $(package)_cppflags
-  $(package)_config_env
-  $(package)_build_env
-  $(package)_stage_env
-  $(package)_build_opts
-  $(package)_config_opts
-
-The *_env variables are used to add environment variables to the respective
-commands.
-
-Many variables respect a debug/release suffix as well, in order to use them for
-only the appropriate build config. For example:
-  $(package)_cflags_release = -O3
-  $(package)_cflags_i686_debug = -g
-  $(package)_config_opts_release = --disable-debug
-
-These will be used in addition to the options that do not specify
-debug/release. All builds are considered to be release unless DEBUG=1 is set by
-the user.
-
-Other variables may be defined as needed.
-
-Build commands:
-
-  For each build, a unique build dir and staging dir are created. For example,
-  work/build/mylib/1.0-1adac830f6e and work/staging/mylib/1.0-1adac830f6e.
-
-  The following build commands are available for each recipe:
-
-  $(package)_fetch_cmds:
-    Runs from: build dir
-    Fetch the source file. If undefined, it will be fetched and verified
-    against its hash.
-  $(package)_extract_cmds:
-    Runs from: build dir
-    Verify the source file against its hash and extract it. If undefined, the
-    source is assumed to be a tarball.
-  $(package)_preprocess_cmds:
-    Runs from: build dir/$(package)_build_subdir
-    Preprocess the source as necessary. If undefined, does nothing.
-  $(package)_config_cmds:
-    Runs from: build dir/$(package)_build_subdir
-    Configure the source. If undefined, does nothing.
-  $(package)_build_cmds:
-    Runs from: build dir/$(package)_build_subdir
-    Build the source. If undefined, does nothing.
-  $(package)_stage_cmds:
-    Runs from: build dir/$(package)_build_subdir
-    Stage the build results. If undefined, does nothing.
-
-  The following variables are available for each recipe:
-  $(1)_staging_dir: package's destination sysroot path
-  $(1)_staging_prefix_dir: prefix path inside of the package's staging dir
-  $(1)_extract_dir: path to the package's extracted sources
-  $(1)_build_dir: path where configure/build/stage commands will be run
-  $(1)_patch_dir: path where the package's patches (if any) are found
-
-Notes on build commands:
-
-For packages built with autotools, $($(package)_autoconf) can be used in the
-configure step to (usually) correctly configure automatically. Any
-$($(package)_config_opts) will be appended.
-
-Most autotools projects can be properly staged using:
-  $(MAKE) DESTDIR=$($(package)_staging_dir) install