Removed `_LEXERPATH`.
Removed `_L._EXISTS()`; core/locale.lua
Renamed Adeptsense image fields.
Renamed editing module's `STRIP_WHITESPACE_ON_SAVE` to `STRIP_TRAILING_SPACES`.
`_M.textadept.editing.block_comment()` supports block comment delimiters.
Also integrated comment strings into `_M.textadept.editing.comment_string` so
block commenting works out of the box.