allow specifying explicit from and to parameters
rename to fromSeqNo and toSeqNo, add to api docs
As per https://github.com/sockethub/sockethub/pull/168#issuecomment-42537481
change imapSeqNo parameters as discussed in Dusseldorf
Merge pull request #168 from sockethub/imap-fetch-from-to

allow specifying explicit from and to parameters