* Add basic achievements functionality.
This reads the mainline achievements.cfg and then all the achievements of each installed add-on.
This is intentionally handled separately from other WML loading so that:
a) All achievements and their status are able to be displayed on the main menu right after Wesnoth starts and regardless of which add-ons are active.
b) Add-ons can add additional achievements to other content, whether UMC or mainline. For example, a modification that adds more achievements for mainline campaigns.
Marking something as achieved is handled by the new [set_achieved] tag and whether an achievement has been completed can be checked via [has_achievement].
There is no attempt to prevent people from manually editing which achievements they've accomplished.
NOTE: These are *not* in any way related to Steam achievements!
- The t_string type is now a schema built-in type and no longer attempts a regex match.
- You can also specify that non-t_string types may be optionally-translatable; this case supports a regex match on the string (but note that the translation mark is not part of the match).
- Error messages involving keys with very large values ( > 128 characters) will now truncate the value.
- To account for occasional cases where the schema is intentionally violated, the --validate command-line option now automatically defines the SCHEMA_VALIDATION preprocessor define.
A key validates as type t_string if one of the following is true:
- The key is not present
- The key has at least one segment with a translation mark
- The key is blank (an empty string)
Any type other than t_string is not allowed to be translatable by default, unless you specify allow_translatable=yes in the [type] tag.
An optionally-translatable string could also be defined as a union of t_string and some other type.
