Flexible name matching

[chaowlert]

Fix #49

Pls merge #56 before reviewing this issue.

This PR allows match property names with different convention. Usage is

TypeAdapterConfig.GlobalSettings.Default.NameMatchingStrategy(NameMatchingStrategy.Flexible);

or

TypeAdapterConfig<Foo, Bar>.NewConfig().NameMatchingStrategy(NameMatchingStrategy.Flexible);

By defining as flexible, it will allow to match between PascalCase, camelCase, lower_case, and UPPER_CASE. This feature is applied to both property mapping & class flattening. And users can defined their own convention (ie, prefix, suffix, replace) by create new NameMatchingStrategy.

[chaowlert]

@BuzzDee3000 Could you kindly test this feature whether it is what you want or not?

[BuzzDee3000]

@chaowlert I will check this asap.