Allow passing a callable to extract()

[akx]

This makes it much easier to do create custom extraction machinery without having to bother with external configuration files or Setuptools entry points.

[sils]

@akx hey, thanks for trying to help us! Please note that we're short of manpower, if you'd like to help please also consider reviewing other peoples PRs.

Your commit seems not to be compatible with Python 3.3 and lower, see https://travis-ci.org/python-babel/babel/jobs/97957737 . Could you fix that?

[akx]

My bad for not running tests on Py3! (Turns out it was an one byte fix ("" to b"").

Anyway, I'd be glad to help in other ways too. :)

[sils]

@akx awesome, just pick one or a few of https://github.com/python-babel/babel/pulls?q=is%3Aopen+is%3Apr+label%3A%22%283%29+pending+review%22 , if you think the PR is good for the project, drop a comment. General rules, all tests must pass of course, more coverage is good, good commit messages are valued.

[codecov-io]

Current coverage is 83.44%

Merging #289 into master will increase coverage by +0.06% as of 0fe3701

@@            master    #289   diff @@
======================================
  Files           22      22       
  Stmts         3756    3758     +2
  Branches         0       0       
  Methods          0       0       
======================================
+ Hit           3132    3136     +4
  Partial          0       0       
+ Missed         624     622     -2

Review entire Coverage Diff as of 0fe3701

Powered by Codecov. Updated on successful CI builds.

[sils]

Thanks! Added note to https://github.com/python-babel/babel/wiki/CHANGES

[sils]

@akx you might want to join our chat at https://gitter.im/python-babel/babel :)