Export minpack API via bind(c)

[awvwgk]

Define C API of minpack:

• declare exports to C for procedures used in SciPy:
  • hybrd as minpack_hybrd
  • hybrj as minpack_hybrj
  • lmder as minpack_lmder
  • lmdif as minpack_lmdif
  • lmstr as minpack_lmstr (not used in SciPy)
  • chkder as minpack_chkder
• wrapper procedures (not used in SciPy) are also exported
  • hybrd1 as minpack_hybrd1
  • hybrj1 as minpack_hybrj1
  • lmder1 as minpack_lmder1
  • lmdif1 as minpack_lmdif1
  • lmstr1 as minpack_lmstr1
• c-compatible callback prototypes
  • minpack_func callback used by minpack_hybrd / minpack_hybrd1
  • minpack_func2 callback used by minpack_lmdif / minpack_lmdif1
  • minpack_fcn_hybrj callback used by minpack_hybrj / minpack_hybrj1
  • minpack_fcn_lmder callback used by minpack_lmder / minpack_lmder1
  • minpack_fcn_lmstr callback used by minpack_lmstr / minpack_lmstr1
• utility function minpack_dpmpar to access machine constants
• use value instead of intent(in) for export if possible
• all C procedures accept a void* data pointer which is available in the callback

Open for discussion:

• include keyword names in C prototypes? (currently not included)

Todo:

• add tests for C API (just port Fortran tests to C?)

  • test minpack_hybrd
  • test minpack_hybrd1
  • test minpack_hybrj
  • test minpack_hybrj1
  • test minpack_lmder
  • test minpack_lmder1
  • test minpack_lmdif
  • test minpack_lmdif1
  • test minpack_lmstr
  • test minpack_lmstr1
  • test minpack_chkder

Closes #15

[ivan-pi]

Is there a good reason to export dpmpar?

[awvwgk]

Needed them to write the tests in C, as there is not really an equivalent available there.

[awvwgk]

Has anyone time to contribute a test or two for the C-API? We should at least test the simplified drivers before merging this PR.

[ivan-pi]

Sure, I'll see if I can make a test or two for hybrj(1) and and lmdif(1).

[awvwgk]

This PR is ready to go, we now have full coverage of the C API.

[awvwgk]

I'll go ahead and merge this PR. We can always change things later if there is something missing.