cleaning and improvements

[videlec]

• split source files

  • PARIInterface.c : exposed functions into GAP
  • conversions.c : conversion between PARI GEN and GAP Obj
  • functions.c : PARI function wrappers

• get rid of C wrappers: FuncPARI_POL_GALOIS_GROUP, FuncPARI_POL_FACTOR_MOD_P, FuncPARI_MULT, FuncPARI_FACTOR_INT, FuncPARI_gcdii (in particular fixes https://github.com/gap-packages/PARIInterface/issues/18)

• GAP -> PARI conversions

  • rename INT_TO_PARI_GEN -> PARI_INT
  • implement PARI_FRAC
  • implement a generic PARI conversion

• get rid of PARI_GEN_ROUNDTRIP (tested more directly in tst/generic.tst instead)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.30%. Comparing base (f2dc31c) to head (8ff9b27). Report is 14 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #20 +/- ## ========================================== - Coverage 92.15% 91.30% -0.86% ========================================== Files 2 2 Lines 51 46 -5 ========================================== - Hits 47 42 -5 Misses 4 4 ``` | [Files](https://app.codecov.io/gh/gap-packages/PARIInterface/pull/20?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gap-packages) | Coverage Δ | | |---|---|---| | [gap/PARIInterface.gd](https://app.codecov.io/gh/gap-packages/PARIInterface/pull/20?src=pr&el=tree&filepath=gap%2FPARIInterface.gd&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gap-packages#diff-Z2FwL1BBUklJbnRlcmZhY2UuZ2Q=) | `100.00% <ø> (ø)` | | | [gap/PARIInterface.gi](https://app.codecov.io/gh/gap-packages/PARIInterface/pull/20?src=pr&el=tree&filepath=gap%2FPARIInterface.gi&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gap-packages#diff-Z2FwL1BBUklJbnRlcmZhY2UuZ2k=) | `88.57% <ø> (-1.18%)` | :arrow_down: |