my-kmacros.el: org-clock-to-hourrow (convert org clock to latex \hourrow)

For invoicing.

Change-Id: I88302f82135509c00ba6cc4142441e51323c6e8c
my-util.el: my-hours-minutes-to-decimal

Convert "1:45" => 1.75.

Change-Id: Iada98badf99f2aeb8ab359dd141bc4b34f629e94