Upper camel case regexp in ErrorType is not valid

[mateuszlitwin]

It does not accept single uppercase letter (https://github.com/palantir/http-remoting-api/blob/develop/errors/src/main/java/com/palantir/remoting/api/errors/ErrorType.java#L33), e.g. "Foo:B" will not be a valid error name.

Regexp like ([A-Z]([a-z0-9]+[A-Z])*[a-z0-9]*) could solve this issue.

[qinfchen]

@divath, I believe that is intentional. We want the error type names to be concise and self-describable.