Logging classes

[obiwac]

Resolves #12.

Will make it into v0.3.0.

To do:

• Implement logging classes (and replace components with this entirely).
• Remove __func__ logging (rationale is that filename/line number sufficient).
• Way to ignore UMBER_LVL_FATAL messages for a class? -> Elegant solution in UMBER_LVL_NEVER.
• Shorten LOG_* macros?
• Think about if we should preserve the UMBER_BLACKLIST/UMBER_WHITELIST environment variables or just do everything with the new UMBER_LVL syntax now. -> UMBER_WHITELIST can be emulated by UMBER_LVL=*=never,class=verbose and UMBER_BLACKLIST can be emulated by UMBER_LVL=class=never, so we bing chillin.
• Add and update tests. -> Didn't add many new tests, but this is simple enough that I'll just add regression tests if I run into issues, whatever.
• Update documentation.