Implement diagnostic SA1300 ElementMustBeginWithUpperCaseLetter

It's hard to tell if the rules used by this implementation are an exact match to the original StyleCop rule. In particular, the following are open questions.

1. What about a class named `fooNativeMethods`? Current behavior: warning unless `fooNativeMethods` is inside a containing `NativeMethods` class.
2. Are private methods included or excluded from analysis? Current behavior: included.
3. How does the `protected internal` accessibility apply to analysis of fields? Current behavior: not considered "internal", and not considered "private".