String literals drop the backslash of unrecognized escape sequences

[Nuhiat-Arefin]

Escape sequences that the string-literal parser does not recognize lose their backslash. Python/Jinja2 keep the backslash of an unrecognized escape.

Reproduction

Template bytes: {{'\\\}'}}

Jinja2 renders \\} (two backslashes followed by a brace). ginger renders \}.

Inside a larger string, {{'\\\{N__xvada_ignored_ws_v1}'}} renders \\{N__xvada_ignored_ws_v1} in Jinja2 and \{N__xvada_ignored_ws_v1} in ginger.

Root cause

src/Text/Ginger/Parse.hs:1285-1304: after the named escapes (\n, \r, \b, \v, \0, \t), the catch-all at line 1303 returns the escaped character without the backslash.