Support nlopt

[oooo26]

• Add submodule nlopt
• Add a simple test for nlopt: abess.pybind_cabess.foo()

[codecov[bot]]

Codecov Report

Merging #414 (f86b149) into develop_cmake (ef57b28) will not change coverage. The diff coverage is n/a.

@@              Coverage Diff               @@
##           develop_cmake     #414   +/-   ##
==============================================
  Coverage          97.31%   97.31%           
==============================================
  Files                  9        9           
  Lines               1079     1079           
==============================================
  Hits                1050     1050           
  Misses                29       29           

Flag	Coverage Δ
Python	97.31% <ø> (ø)

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