Multi-line value support

Some valve implementations (there are several... 👎 ) support multi-line values (exclusively using the '\n' character).
Hammer variations are a good example that support vmfs with this feature in pre-CSGO versions, yet post-CSGO versions will crash.

This library currently doesn't newlines, but it should do

Start by locating the parser handling values and reproduce the issue with a Hammer-style value containing literal newline characters. Done means the library accepts multi-line values without crashing and preserves their newlines; no source file or test is named in the issue.

Written by the indexing model from the issue text.