Add a Requirements section to Readme

Thanks Kenji Rikitake.
Add EDOC_OPTS variable.

This is useful if edoc can't process the sources without using the
Erlang pre processor, for instance, or to pass other custom options
when building the documentation.
Add relx improvements

Add ability to config relx in-line options by setting RELX_OPTS
Fix using RELX_CONFIG variable
Use relx 0.5.0
Merge branch 'master' of git://github.com/kaos/erlang.mk
Bump relx version to 0.5.2
Changed \s pattern in sed regex pattern to [[:space:]]. This should make the sed pattern portable across GNU and BSD implementations.
Add --no-check-certificate to wget to make it work on default OSX
Merge branch 'master' of git://github.com/kiela/erlang.mk
Merge branch 'master' of git://github.com/NineFX/erlang.mk
Append DEPS_DIR at the end of ERL_LIBS if ERL_LIBS is defined

Only done if DEPS_DIR isn't found in it yet.

Thanks to Sean Chalmers for the debugging and original fix.