If a g:table_mode_separator is escaped by a backslash, the table is
aligned ignoring this instance of the g:table_mode_separator, but the
column deletion and insertion functions did not consider this behaviour.
The g:table_mode_escaped_separator regex is simplified and optimized a
little bit. Also more care is taken to prevent unexpected behaviour if
special characters are used as g:table_mode_separator.
Initial support. Alignment and border creation is fixed and is
consistent in considering the escaped table separator as part of the
column.
TODO :
* Fix syntax to reflect the above.
* Fix cell definition, motion & formula engine to incorporate this.
