Tmuxp

- 137 Support for environment settings in configs, thanks
`tasdomas`
- Spelling correction, thanks [sehe].

- 135 Load multiple tmux sessions at once, thanks [madprog].
- 131 133 README and Documentation fixes

- switch to `.venv` for virtualenv directory to not conflict
with `.env` (used by [autoenv]).
- 130 move to [entr(1)] for file watching in tests. update docs.
- [compatibility] Support [Anaconda Python] 2 and 3

- 122 Update to support tmux 2.1, thank you [estin].
- use travis container infrastructure for faster tests
- change test in workspace builder test to use `top(1)` instead of
`man(1)`. `man(1)` caused errors on some systems where `PAGER` is set.

- 119 Add fix python 3 for [sysutils/pytmuxp] on FreeBSD ports.
See GH issue 119 and [201564] FreeBSD Bugzilla. Thanks Ruslan
Makhmatkhanov.

- Renamed `config.expandpath` to `config.expandshell`.
- compat 2.7/3.3 wrapper for `EnvironmentVarGuard` for
testing.
- You can now use environment variables inside of
`start_directory`, `before_script`, `shell_command_before`,
`session_name` and `window_name`.
- [examples]: add example for environmental variables,
`examples/env-variables.json` and `examples/env-variables.yaml`.
- 110 de-vendorize [colorama].
- 109 fix failure of test_pane_order on fedora machines from
[marbu]
- 105 append `.txt` extension to manuals (repo only)
from [yegortimoshenko].
- 107 Fix Server.attached_sessions return type by
[thomasballinger].
- update travis to use new tmux git repository.