Add a lenient mode

[hegemonic]

Before I can integrate Catharsis into JSDoc, the parser needs to support a lenient mode that's a little more forgiving than Closure Compiler.

When in lenient mode, the parser should support the following patterns, which have worked in JSDoc 3 for a while:

• Allow function without trailing parens.
• Allow type applications without a period (for example, Array<string>).
• Allow type unions without parens (for example, string|boolean).
• Allow name expressions to contain # and ~, which JSDoc uses to indicate scope. (I think this should only be allowed in lenient mode, although I'm not certain...)

Also, we should maintain separate type caches for lenient-mode and strict-mode parsing.

[hegemonic]

A couple more changes for lenient mode, which is now extremely lenient indeed:

• Parse failures no longer result in an exception. Instead, Catharsis pretends that your bogus type expression was a valid name expression.
• The keys for JavaScript record types should be strings; if you don't use a string, JavaScript will just coerce your chosen value to a string. Catharsis doesn't quite enforce this rule, but it now expects you to use a name expression for the key. In lenient mode, you can still use any type you want for the key.

[hegemonic]

This change caused the tests to take about twice as long as before. I don't have good benchmarking data, so I'm not sure whether this is an across-the-board speed hit or whether it affects certain types more than others.

Based on when I first noticed the slowdown, I'm pretty sure that the culprit is type unions without parentheses.