Reimplement 8 matrix functions in C

- Slap.Mat.fill
- Slap.Mat.copy
- Slap.Mat.geband_dyn/ungeband
- Slap.Mat.syband_dyn/unsyband
- Slap.Mat.luband_dyn/unluband
Reimplement two functions on vectors in C

- Slap.Vec.copy
- Slap.Vec.fill
Refactor slap_mat_fill in C
Improve slap_mat_copy_stub in C

The current version of slap_mat_copy_stub calls ?lacpy of LAPACK.
Merge branch 'c-impl' into travis-ci
Remove 'allow_failures' from .travis.yml