Skip appup generation for new app in release

fix erlexec parameter

look for new and old versions in the target parent

default module appup instruction -> load_module

The target_dir config in reltool allows you to put your release in
a directory other than in ./NAME, so we should look in the parent
directory of that to find the new and old versions instead of
simply looking in ./

Move untaring and retaring into a temporary path instead of in ./
to prevent name collisions with "releases" and "lib" that might
exist already. Having a subdirectory rel/releases/ can be useful.

Allows customizing the arguments handed over to the Erlang VM, e.g. to
set a name or a cookie, e.g. by setting escript_emu_args to:

%%! -name rebar -setcookie rebar

Use "%~f0" to get the full path of rebat.bat to correctly locate the
rebar script. Also put the script name in quotes when passing it to
escript.exe to correctly handle paths with spaces.

Add command listing for list-deps

Recursively search "src" for .proto files

Allow plugins to run before/after a rebar command.

- Port compiler no longer requires bash on windows.
- It's possible to use compilers whose command lines don't fit into
  the default template

Calling erlang:system_info(wordsize) yields the internal word size of
the Erlang emulator. But due to the halfword emulator, need to pass
{wordsize, external} instead to get the word size, or pointer size, as
seen by external code such as NIFs. The halfword emulator has 4 byte
internal words but 8 byte external words due to 64-bit compilation,
which means NIFs for the halfword emulator also have to be compiled
64-bit. But just passing wordsize is equivalent to passing {wordsize,
internal}, which does not indicate the pointer size for the halfword
emulator.

Older versions of Erlang do not support {wordsize, external}, though,
so continue to pass just wordsize for those versions.