Simple open bracket and double quote paired insertion
opening_insertion improvments
Quote insertion must be handled on its own
Extract unpaired bracket counter
Make bracket_count ignore ignored scopes
Simple backspace_insertion implementation
Don't insert leading space after a macro or dispatch char
++todo
Revert "Use a best-effort top_form search when g:sexp_maxlines == -1"

This reverts commit 08ea48afa0dba2c61d8fff14e2e842349ff77112.

Besides being buggy, maintaining two different kinds of behavior for
g:sexp_maxlines is burdensome.
Revert "Don't call s:move_to_top_bracket() if we don't have to"

This reverts commit 3e71332c15c42e3b991c7592ce6f57ac59d222ba.

Another optimization related to last revert
Refactoring for style
Expand string scope to include regexps and "patterns"
Add , to clojure macro characters
Implement s:closing_insertion()
Implement sexp#quote_insertion
Test previous column for syntax when inserting keys

The position under the cursor in insert mode may fall outside a syntax
region, so we must test the previous position
Add double quote handling to sexp#backspace_insertion
Avoid expensive searchpairpos() when possible
Always skip over the current ket if found
Use current bra when searching backwards for opening bra