Added the ability to run builtin commands in xpd files

This allows the xpd files to use xpd as platform, and other tools for any
needed actions during builds.
Added the ability to append environment variables in package commands

This allows xpd package commands in the form of:

build:
  env:
    LDFLAGS: "-static"
  cmds:
    - make bin
    - make all

For right now it assumes appending uses spaces for separate, not " ". It
might be best to to just force the user to supply the padding.
Updated patchelf to be built statically so we can use it no matter the libc

The really needs to work no matter what the current libc setup, so a static
build is the only way.
Add some notes on other similar project.

disthash is very, very similar to xpkg.  Although they are more focused
on pure source builds and not binary redistribution.  I should look more
closely at that the project and see if it can be adapted to fit my needs,
or at least to leverage some concepts.
Added lists to hashstack and win-builds, both good lists of packages

If xpkg is to be useful we need to have these packages.  The good news is
that hashstack packages are yaml based so they can be auto-converted to xpd
files.
Make interpolation of variables in advanced commands recursive.

This allows for support for usage of special variables anywhere we wish,
working_dir or args.
Add the ability to run builtin commands through the command line program

This is useful for testing some of the more complex commands.
Add the patchelf command to edit the LD_INTERP of elf binaries

Some programs don't obey the linker flags to point to the correct interp,
so we use this command to fix them up.
Update GCC package to use patchelf so that it's LD_INTERP points to our link

This link is use to route to which ever ld.so binary should be used.
Parallize install across several packages

These take a while, no need to wait on them.
WORK IN PROGRESS