refactor hints by pulling out into separate classes

Also expose some ExpressionParser methods for them to use
refactor hints by pulling out into separate classes

Also expose some ExpressionParser methods for them to use
Merge branch 'hint-refactoring' of https://github.com/Porges/PowerAssert.Net into hint-refactoring
add float equality hint
specialized checks for string compares
Also check format chars
add a check for broken equality implementation
checks for mistakes using timespan
Tests for "Broken Equality" hint
clarify comment
make resharper more happy about tests
Tests for delegate invocation hint
tidy usings
ignore *.cache files that R# now generates
Add tests for the enumerable-equals hints
Flesh out tests
Add some flipped versions of symmetric tests

To improve code coverage, mainly.
Merge pull request #4 from Porges/hint-refactoring

Hint refactoring