Define `zap-to-string` command.

This command works exactly like the (advised) version of `zap-to-char` I
am using, but it let's me enter a string to zap to (instead of a single
char).
Start using idle-require.
Fix some small formatting inconsistencies.
Add basic customizations for ample theme.
Add custom command for removing all empty lines from current buffer.
Add custom command for sorting and uniquifying lines in current buffer.
Start using projectile.
Start using loccur.
org-mode: Apply emphasis mark-up even if it is followed by an opening
square bracket.

This keeps mark-up from breaking if marked-up element is followed by a
footnote.

cf. f016f8d
Highlight portions of lines that exceed `fill-column` in org-mode and
prog modes.