Refactored functions involving digits.
Initialize cofactor in the twist.
New benchmarks for new functions.
Prototypes for new utility functions.
Add tests for point at infinity.
Make tests more comprehensive.
Small adjustments in tests.
Add preset for supersingular curves.
Restore workint version of pp_dbl_k2_projc_lazyr().
Merge pull request #2 from relic-toolkit/master

resync with relic-toolkit:master