[bash-completion] Fix #668

Handle uppercase letters in program names. This also deals with `-` and
`.`, both of which are quite common in program names, e.g., `xdg-open`
and `foo.sh`.

Close #669

You can use your mouse or binadble preview-up and preview-down actions
to scroll the content of the preview window.

    fzf --preview 'highlight -O ansi {}' --bind alt-j:preview-down,alt-k:preview-up

Related #666

Fix #666

Related: #660

Use hard-coded limit to keep it simple. An alternative is to dynamically
calculate the width of the visible area and use it as the limit, but it
can cause unwanted truncation of the query on screen resize/split.

Fix typo in comment

[fzf-tmux] Make fzf target correct session in group

Fixes #643
Doesn't break #648

This reverts commit 4d444777.

[fzf-tmux] Fix grouped tmux session confusion

[zsh-completion] Split default zsh binding at the correct place

Avoids confusing grouped sessions.
Fixes #643

The command substitution and following word splitting to determine the default
zle widget for ^I formerly only works if the IFS parameter contains a space. Now
it specifically splits at spaces, regardless of IFS.

Related #642

Fix #520
Fix junegunn/fzf.vim#42

fzf#wrap([name string,] [opts dict,] [fullscreen boolean])

- Make structs smaller
- Introduce Result struct and use it to represent matched items instead of
  reusing Item struct for that purpose
- Avoid unnecessary memory allocation
- Avoid growing slice from the initial capacity
- Code cleanup

By only using leaf functions

Sort performance increases as the size of each sublist decreases (n in
nlog(n) decreases). Merger is then responsible for merging the sorted
lists in order, and since in most cases we are only interesed in the
matches in the first page on the screen so the overhead in the process
is negligible.

https://golang.org/doc/go1.5