Update startup script to allow overriding config location.
Ignore rebar if it needed to be downloaded.
Merge pull request #155 from rlipscombe/rl-override-config

Allow VMARGS_PATH and CONFIG_PATH to be overridden
Give release scripts ability to handle directories with spaces
Merge pull request #154 from nuex/quote_vars

Give release scripts ability to handle directories with spaces
Windows support
Windows build instructions
Merge pull request #159 from nuex/windows

Windows Support
Add support for explicit erts path

Add support for 'include_erts' to be defined as a path to an external erlang
release.  This will allow for relx to include cross-compiled erts builds.

include_erts can now be one of three values: true (default), false, or
"/path/to/erlang".

The symantics do not change unless it is set to a string in which case
it only overrides the default lookup "code:root_dir()" with the given
path.
Merge pull request #160 from zerotao/explicit_erts

Add support for explicit erts path