`class foo_bar` should result in `struct Foo_Bar`

[iphydf]

In apidsl, the underscore is used as namespace separator, but is also permitted inside identifiers. Class names are capitalised, but the toxcore naming standard is "underscore-separated capitalised words" for struct names. Apidsl should implement this naming standard.

Alternatively, and possibly this is a better option, we give the user the freedom of how to spell their struct name, and lowercase it for the namespace name (in function names). This is somewhat necessary for what is currently called class toxAV (struct ToxAV), which, if spelled class tox_av would be struct Tox_Av, which may not be desirable. If we want the naming standard to be "abbreviations are all-caps" instead of the Java convention of "abbreviations are words", it should be class Tox_AV and struct Tox_AV with function prefix tox_av_. The same would go for class Tox_QNL, which would currently be class tox_QNL which is ugly, or class tox_qnl which would result in struct Tox_Qnl.