Fix issue when two filter "excludes" have the same string length

[DefaultRyan]

Found an issue where supplying multiple excludes with the same length caused bad behavior in Release and asserts in Debug.

Added test cases, and the second test case, "filter_excludes_same_length" was hitting an assert in debug due to a malformed sorting predicate in the filter class. In the test case, both compare({"N.N3", false}, {"N.N4", false}) and compare({"N.N4", false}, {"N.N3", false}) would return true, violating sorting constraints.

For the curious, std::sort (and the other C++ sortings I can think of) require a Strict Weak Ordering. What this means in C++ terms is, given a comparison object compare, the following requirements must be met:

• compare(a, a) == false for all a
• If compare(a, b) == true then compare(b, a) == false
• If compare(a, b) == true and compare(b, c) == true then compare(a, c) == true
• If compare(a, b) == false and compare(b, a) == false and compare(b, c) == false and compare(c, b) == false then compare(a, c) == false and compare(c, a) == false (aka transitivity of equivalence)

Fixes #21

[kennykerr]

Looks good to me. @Scottj1s may also want to take a peek.

[roywill]

[Scottj1s]

Thanks Ryan, and for adding test cases