Tmuxp

- Bump libtmux to 0.8.0
- 264 Update license from BSD to MIT
- 348 Continuous integration updates and fixes for Travis CI

- Update builds to use trusty
- Remove older python 3 versions (before 3.6)
- Update pypy versions

- 349 flake8 via continuous integration
- Improve reliability of time-sensitive tests by
using `while True` with a timeout.
- Update sphinx to 1.7.1
- Update alagitpull (sphinx theme) to 0.0.19.
External websites open in new window.
- Update pytest to 3.4.1

- 312 Support for tmux 2.6 layout setting (via hooks) in the
following scenarios:

- loading outside tmux
- loading inside tmux, via switch-client
- loading inside tmux, with session in background (with -d), and
reattaching/switching to after
- loading session outside tmux in background with -d, and
reattaching/switching after

- 308 Fix bug where layouts don't correctly set on tmux 2.6
- Upgrade libtmux to 0.7.7

- `before_script` now respects `start_directory`
in the session root. This makes it easier to run things like `pipenv install` as a `before_script`.

- Update libtmux to 0.7.5 for tmux 2.6 hotfix

- 184 - update libtmux to fix environmental variables in the
session scope
- Update libtmux to 0.7.4
- Updates to pytest and pytest-rerunfailures

- 252 Fix bug where loading a session with a name matching a subset
of current session causes undesired behavior.
- Update libtmux to 0.7.3
- Switch theme to alagitpull (alabaster subtheme)
- Remove unneeded doc dependency packages