Adds Fday_date field to calculate Falternating_day. Refs #9.
Tests external access of Fday_date field. Refs #9.
Adds proc to recalculate alternating_day value. Refs #9.
Exports alternating_day field to C API. Refs #9.
Adds changes_day attribute to entries. Refs #9.
Adds formatting of dates with a part shadowed. Refs #9.
Uses generic id for multiplatform code. Refs #9.
Documents task in changes log. Refs #9.

Also bumps version number to correct development value.
Merge branch 'feature/t9_alternating_bool'