This avoids the problem in which :FZF command silently fails when fzf
executable cannot be found in $PATH of the hosting tmux server.

/cc @Tranquility

Related: #135

0.9.4

When fzf works in filtering mode (--filter) and sorting is disabled
(--no-sort), there's no need to block until input is complete. This
commit makes fzf print the matches on-the-fly when the following
condition is met:

    --filter FILTER --no-sort [--no-tac --no-sync]

or simply:

    -f FILTER +s

This removes unnecessary delay in use cases like the following:

    fzf -f xxx +s | head -5

However, in this case, fzf processes the input lines sequentially, so it
cannot utilize multiple cores, which makes it slightly slower than the
previous mode of execution where filtering is done in parallel after the
entire input is loaded. If the user is concerned about the performance
problem, one can add --sync option to re-enable buffering.

- Key bindings for bash, zsh, and fish
- Fuzzy completion for bash (file, dir, process)

DISCLAIMER: This is a backward incompatible change

Fix Travis CI build

Update outdated --help output

Improve `find` command for ALT-C: exclude proc/dev

When using the widget in "/", it would descend into 'dev/'.
Using '*' for the starting path would do so also with the new '-fstype'
excludes.

`cut -b3-` and `sed 1d` have been added to massage the different format
of the list.

This also uses `-L` with all calls to find, especially for the file
finders.

Ref: https://github.com/junegunn/fzf/pull/122

Related: 8bead4ae