Add utility to compare enums to Strings

[sleberknight]

The basic Java Enum class does not have methods to compare against CharSequence, e.g. that come from user input in a web form or similar. For example, I'd like to be able to do this:

// userSuppliedColor is a String
if (Color.RED.equalsString(userSuppliedColor)) {
    ...
}

or this:

if (Color.RED.equalsStringIgnoringCase(userSuppliedColor)) {
    ...
}

Alas, Java doesn't provide such methods, and amazingly I cannot find anything that does this in Google Guava or Apache Commons. It seems like this is something relatively common to want to do. Anyway, I guess we'll add our own which will at a minimum allow:

• comparisons of a single enum constant to a CharSequence in either case-sensitive or case-insensitive manner
• comparison of a CharSequence against multiple enum constants in case-sensitive or case-insensitive manner