After the change in 1d340dcc77,
there was some grumbling in gitter that `SPC L` is not as convenient
as `SPC l`. Apparently avy-goto-line is a popular function.
`SPC y` is chosen because it is:
- currently unused (as far as I can tell).
- sort of mnemonic because "avy" has a "y" in it.
- doesn't require SHIFT to type
- is accessible even on non-US keyboards
(there were suggestions such ";" and "\" that are not as accessible
on non-US keyboards)
This change also updates the documentation regarding the change from
ace-jump-mode to avy.
Helm seems to treat "!" specially in pattern matching, so having a ! in
the pattern string when traversing directories is problematic. This
change fixes#2737, because as far as I can tell "+" has no special
meaning in a helm pattern.
Of course, we can choose a different character, but I'm fond of "+" as
representing "more layers here".
