Standardize header file names

[saraedum]

we are trying to standardize the naming of header files in all flatsurf projects. Namely, project.h(pp) should include the entire API and local.hpp should contain generated setup such as macros for cling.

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• Header file e-antic.h is now called local.h. There is still a header file e-antic.h that includes all of e-antic's C interface, so in particular local.h.
• Header file renfxx_fwd.hpp is now called forward.hpp. The old header file renfxx_fwd.hpp can still be used.
• Header file renfxx.h is now called e-antic.hpp. The old header file renfxx.h can still be used.

[codecov[bot]]

Codecov Report

Merging #203 (dfd6625) into master (9cde33b) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #203   +/-   ##
=======================================
  Coverage   92.10%   92.10%           
=======================================
  Files         105      105           
  Lines        2052     2052           
=======================================
  Hits         1890     1890           
  Misses        162      162           

Impacted Files	Coverage Δ
libeantic/e-antic/renf_class.hpp	100.00% <ø> (ø)
libeantic/e-antic/renf_elem.h	100.00% <ø> (ø)
libeantic/e-antic/renf_elem_class.hpp	100.00% <ø> (ø)
libeantic/srcxx/renf_elem_class.cpp	97.69% <ø> (ø)

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[saraedum]

@videlec do you agree to such a renaming?

[videlec]

fine with me