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
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