Executabilize bin/knex

Mark as binary to be installed in package.json; set executable
permission for development convenience.
Create skeleton CLI for migrations
bumping bluebird dependency
Merge branch 'migrations' of github.com:benesch/knex into benesch-migrations

* 'migrations' of github.com:benesch/knex:
  Create skeleton CLI for migrations
  Executabilize bin/knex
continuing work on migrations cli
Merge branch 'master' of github.com:tgriesser/knex

* 'master' of github.com:tgriesser/knex:
  Test for aggregate function with output name.
  Support for multiple aggregate functions.
  Failing test for #108
  Drop default output name for aggregate functions.
Initial version of the migration cli ready