fix NumberFormatException when parsing "ff" alpha value into a Byte
Merge pull request #74 from oliver/master

fix NumberFormatException when parsing "ff" alpha value into a Byte
Add support for SIP addresses

Store SIP addresses of data kind CommonDataKinds.SipAddress
(called "sip_address" in the edit schema) as sip/sips URI's in TEL properties.
"sip" is added to URI's without scheme.

Requires update of ical4j-vcard to allow Telepone properties containing a URI.