Preserve indexes in Functional\zip()

Remove callable typehint from compose() (lstrojny#98)

This is due to lack of support in HHVM.

See facebook/hhvm#6954

lstrojny#95: deprecate invocation of (lstrojny#96)

Adding capture()

Merge pull request lstrojny#62 from lstrojny/features/poll-retry

First version of F\retry() and F\poll()

Fix lstrojny#55

Allow resetting F\memoize() by passing null as a callback

Adding debug flag for phpunit

Fixing F\flatten() for objects

Fixing signature