Feature extend julianday

See merge request !8

The usage of flag_std_form needs a thorough cleanup. Additionally, mtime
might want to adopt a workflow in which arguments are normalized at
first and computations are done only after this. This simplify a lot of
cases.

This commit fixes icon/icon#9450 .

1.0.10 Python: 2 to 3,  (dt,dt) / td division, mtime object interface

Closes #28

See merge request !7

Fix bug in struct declaration.

See merge request !6

* The Fortran version must mirror the C version.

Master patched

See merge request !2