This commit adds a new type of enumerator meant to support flag
values. The enumerator parses comma-delimited strings and matches
each string or value to a list of valid flags. Additionally, the
enumerator does some basic checks to see if 1) a flag is valid in the
enumerator, and 2) if any conflicting flags are specified.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>