Added Bug and BugComment classes
Service#xmlrpc_bug_query learned

- to accept more than 1 bug_id
- to accept include_fields as a parameter
RubyBugzilla::Bug learned to normalize attributes
RubyBugzilla::BugComment learned to normalize attributes
RubyBugzilla::Bug learned to parse flags into RubyBugzilla::BugFlag
Style cleanup in response to Rubocop comments
Changed to use newer RSpec expect syntax
Rename classes: BugComment and BugFlag to simpler Comment and Flag.
Renamed Bug#process_attributes to Bug#normalize_attributes
Created RubyBugzilla::Base object.

Bug, Comment and Flag are subclassed from it.
Converted Comment#private? method to accessor and alias
Converted Flag#active? method to accessor and alias
Merge pull request #15 from chessbyte/create_bug_class

Create Bug, BugComment, and BugFlag classes