alpha-6

• ErlyDTL templating replaced by Mustache properly (some bugfixes)
• Size of rebar3 script cut roughly in half
• rebar3 shell has received an overhaul and now has an agent running (r3:do(compile))
• package handling overhaul (including checksum verifications and local disk cache)
• much better plugin handling
• bugs fixed in handling upgrading and lock files
• bug fixes related to path-handling
• fixes to hooks and tests
• addition of options to exclude apps, add various source directories
• tar and release commands are now hookable
• better error reporting
• more bug fixes