Fix the strashCode; add benchmark

Thanks to Evan Cordell who spotted a problem with the strash code colliding.
Interesting, as it has a strong impact on the logic/c performance
(but none on solving).

See #17

Merge branch 'master' of https://github.com/go-air/gini

s/irifrance/go-air

ditto

ditto

aiger bugfix and usability improvements

This commit fixes a bug in the aiger ascii output for latch values and
adds some usability/performance improvements

For usability, we have added a Write method to gini to have it dump
a dimacs CNF to a writer.

For performance, we have made it so that more learned clauses could be
derived in incremental mode with test scopes when the last solve gave
unsat.

cleanup

- use log.Fatal on failed checkmodel
- propagate BCP below current test level via cleanupSolve return value.
- a bit of formatting

test scope fix/sudoku test formatting

This commit fixes a bug in test scopes related to
solveInit.

Also fixes documentation placement in sudoku_test

Untest on unsat bugfix

This commit fixes a bug in Untest when the last sat call was Unsat.
The conflict on untest results in more derivations during backtracking.
This fix ensures that all unit clauses are propagated.
Previously, the unit clause from derivations during untest backtracking
were not propagated.

Merge pull request #12 from irifrance/m

Incremental Performance Improvements