Close #338

Fixes Helptags! command from fzf.vim

Fix CTRL-T on fish to work asynchronously

Values for 'up' and 'down' can be written with ~ prefix. Only applies
when the source is a Vim list.

    e.g. { 'source': range(10), 'down': '~40%' }

Close #322

This reverts commit c601fc64.

Related #317

Close #317

Close #312

so that it doesn't corrupt file that doesn't end with a new line
character. Close #311.

    > time cat /tmp/list | fzf-0.10.1-darwin_amd64 --ansi -fqwerty > /dev/null

    real    0m4.364s
    user    0m8.231s
    sys     0m0.820s

    > time cat /tmp/list | fzf --ansi -fqwerty > /dev/null

    real    0m4.624s
    user    0m5.755s
    sys     0m0.732s

    > wc -l /tmp/list2
     2594098 /tmp/list2

    > time cat /tmp/list2 | fzf-0.10.1-darwin_amd64 -fqwerty > /dev/null

    real    0m5.418s
    user    0m10.990s
    sys     0m1.302s

    > time cat /tmp/list2 | fzf-head -fqwerty > /dev/null

    real    0m4.862s
    user    0m6.619s
    sys     0m0.982s