Sh

- bugfix where setting `_ok_code` to not include 0, but 0 was the exit code [545](https://github.com/amoffat/sh/pull/545)

- `_env` now more lenient in accepting dictionary-like objects [527](https://github.com/amoffat/sh/issues/527)
- `None` and `False` arguments now do not pass through to underlying command [525](https://github.com/amoffat/sh/pull/525)
- Implemented `find_spec` on the fancy importer, which fixes some Python3.4+ issues [536](https://github.com/amoffat/sh/pull/536)

- regression fix if `_fg=False` [520](https://github.com/amoffat/sh/issues/520)

- minor Travis CI fixes [492](https://github.com/amoffat/sh/pull/492)
- bugfix for boolean long options not respecting `_long_prefix` [488](https://github.com/amoffat/sh/pull/488)
- fix deprecation warning on Python 3.6 regexes [482](https://github.com/amoffat/sh/pull/482)
- `_pass_fds` and `_close_fds` special kwargs for controlling file descriptor inheritance in child.
- more efficiently closing inherited fds [406](https://github.com/amoffat/sh/issues/406)
- bugfix where passing invalid dictionary to `_env` will cause a mysterious child 255 exit code. [497](https://github.com/amoffat/sh/pull/497)
- bugfix where `_in` using 0 or `sys.stdin` wasn't behaving like a TTY, if it was in fact a TTY. [514](https://github.com/amoffat/sh/issues/514)
- bugfix where `help(sh)` raised an exception [455](https://github.com/amoffat/sh/issues/455)
- bugfix fixing broken interactive ssh tutorial from docs
- change to automatic tty merging into a single pty if `_tty_in=True` and `_tty_out=True`
- introducing `_unify_ttys`, default False, which allows explicit tty merging into single pty
- contrib command for `ssh` connections requiring passwords
- performance fix for polling output too fast when using `_iter` [462](https://github.com/amoffat/sh/issues/462)
- execution contexts can now be used in python shell [466](https://github.com/amoffat/sh/pull/466)
- bugfix `ErrorReturnCode` instances can now be pickled
- bugfix passing empty string or `None` for `_in` hanged [427](https://github.com/amoffat/sh/pull/427)
- bugfix where passing a filename or file-like object to `_out` wasn't using os.dup2 [449](https://github.com/amoffat/sh/issues/449)
- regression make `_fg` work with `_cwd` again [330](https://github.com/amoffat/sh/issues/330)
- an invalid `_cwd` now raises a `ForkException` not an `OSError`.
- AIX support [477](https://github.com/amoffat/sh/issues/477)
- added a `timeout=None` param to `RunningCommand.wait()` [515](https://github.com/amoffat/sh/issues/515)

- bugfix for poor sleep performance [378](https://github.com/amoffat/sh/issues/378)
- allow passing raw integer file descriptors for `_out` and `_err` handlers
- bugfix for when `_tee` and `_out` are used, and the `_out` is a tty or pipe [384](https://github.com/amoffat/sh/issues/384)
- bugfix where python 3.3+ detected different arg counts for bound method output callbacks [380](https://github.com/amoffat/sh/issues/380)

- pypi readme doc bugfix [PR377](https://github.com/amoffat/sh/pull/377)