Add support for <target> :<env> instructions in epm config

Adds parser support for filtering directives based on the current
environemnt
More intuitiv cmd parser
Fix support for parsing w/env

+ add some basic encoding
Add support for referencing latests git tag with '_'
tmp
Add basic support for overriding packages

If you need a fix in a deep dependency, just use the ~ operator with the pkg abspath
this will create a callback that will run after all configs are parsed.
Allow for wildcard tag status in epm_git