mb2md converts mbox mailboxes to maildir format

Features:
- converts a user's main mailbox as specified by the MAIL environment variable
- converts a single mailbox into corresponding maildir
- converts multiple mailboxes in a directory into corresponding maildirs
- recursive operation on a given directory
- replaces all occurrences of dots ('.') in a mailbox name by underscores ('_')
- able to handle spaces in mailbox names
- converts mbox files in DOS format (CRLF) to Unix file format
- can strip an extension (e.g. ".mbx") from a mailbox name prior to converting
- uses the Content-Length: header if told to
- removes dummy message that some IMAP servers put at the start of a mailbox
- removes the "From " line that starts every mail in a mailbox
- removes the '>' character from escaped "From " lines
- sets the file date of a message to the date in the message's "From " line
- sets the flags F,R,S,T (flagged, replied, seen, deleted) on the filename of
  the converted message according to the flags found in the Status, X-Status,
  X-Mozilla-Status and X-Evolution headers of the message.
