Can't use semicolons (and therefore html entities) in per-style attribution

The default attribution can be interpreted as html, e.g. when shown in tilejson output

https://github.com/openstreetmap/mod_tile/blob/master/mod_tile.h#L32

It can be overwritten per-style in renderd.conf

https://github.com/openstreetmap/mod_tile/blob/master/renderd.conf#L38

However, this doesn't work if you have any semicolons in your override string, e.g. for ampersands, copyright entities or similar. The role of semicolons in .ini files seems to be implementation-specific as to whether they are a comment delineator only at the start of the line, only when preceded by whitespace, or at any point during the line. Additionally, escape sequences (typically backslash, e.g. ; ) are implementation-specific. At the moment, we have an anywhere-no-escape parser.

Perhaps we need a different ini parser, or a different configuration file format.

Compare the attribution definitions in mod_tile.h and renderd.conf, then trace how the per-style value is parsed before it appears in TileJSON output. Determine how semicolons and HTML entities should be represented without being treated as comments. Done means per-style attribution accepts these values reliably and the chosen configuration approach is validated.