minor, provide a simple sunrise/noon/sunset stream

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, outsource celestial calculations to celest.[ch] and offer an interface for it

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, refactor solar.c in terms of celest's API

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, offer calculation hints to cel_rts() through struct cel_calcopt_s

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, give calculation hints to cel_rts()

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, factor out deg->h conversion in celest.c

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'dso/solar' into next

* dso/solar:
  minor, factor out deg->h conversion in celest.c
  minor, give calculation hints to cel_rts()
  minor, offer calculation hints to cel_rts() through struct cel_calcopt_s
  minor, refactor solar.c in terms of celest's API
  minor, outsource celestial calculations to celest.[ch] and offer an interface for it
  minor, provide a simple sunrise/noon/sunset stream