Added entries to todo.
Cleanup pass.

- Renamed instances of "LeadCodeUnit" to "LeadUnit", as that seems to be the accepted term where I've read.
- Doc updates.
Added named endpoints for the entire surrogate range.
Updated UTF-8 CharSize().

- Both versions of UTF-8's CharSize() now test for the invalid surrogate ranges.
	- These checks are only performed if we've determined that the range of the given character may be in the surrogate range. This reduces the number of compares needed for valid characters.
- The code point version no longer uses IsSurrogate(). It tests for the surrogate ranges directly. This is faster because by the time we get to testing for surrogates, we have a clamped range.