- Replaced time.Now().Sub() with time.Since()
- Replaced unnecessary string/byte slice conversions
- Removed obsolete return and value assignment in range loop

Perl was used to remove the trailing newline character, but fzf already
has --print0 to use null character as terminators, and fish read -z is
expecting null character as terminators. There is no reason to depend on
perl if --print0 is passed to fzf invocation.

(i.e. spawn xterm)

The section is no longer relevant since (G)Vim 8 or above has builtin
terminal emulator.

Fix #1592

A newer version of the sys module is needed for pull request #1341

[bash-completion] Fix custom completion with dynamic loader enabled for non-standard command names (#1564)

Related to #1170.

Fix the solution for commands with non-standard names
where `$cmd` and `$orig_cmd` differ. e.g. `s.foo` -> `s_foo`

Close #1554

Close #1540

Similar to this PR from fzf.vim:
https://github.com/junegunn/fzf.vim/pull/712

Close ##1533

Close #1539

Close #1535

Close #1521

    fzf --color gutter:-1

Close #1529
Close #1468

Fix #1517

Close #1500

Related #1466

Related #1466