Script fragments - resolves issue #42 and #44

[kristianmandrup]

Some major refactoring/cleanup of cli. Tested and works:

$ make build -j
$ bin/ember-script -j --input sandbox/test-fragmented.em
$ bin/ember-script -j --input sandbox/test-exfragmented.em

Also added Changelog and Contributing doc. Take (merge) what you like, but please let's have the fragmentation support and an easier way to play around with cli, than all in one huge chunk of a file.
Cheers :)

[ghempton]

I assume this PR is superseded by #50 ?