unescape characters Grep Tool treats as special but Vim as literal

[Konfekt]

addresses #224

[Konfekt]

One could think about using very magic for the Vim search expression to economize much of this (un)escaping.

[Konfekt]

Anything left to be done? This is useful, for example, if one searched with vim-grepper for lines that match a regular expression containing \b and then wants to jump to the matches in the quickfix list.

[Konfekt]

Good evening @mhinz, @jez or @ddeville, would one of you mind taking a look at this PR that should ease searching for the grepped string in the obtained quickfix list?
At this occasion, how about @mmrwoods 's one as well?