build cglpk with function signatures
version pep440 compliance added, not used yet

Instead of just using the as-is output of git describe, which is
```tag-N-commit```
Now use
```tag.postN-commit```
The option pep440=True will make this pep440 compliant
```tag.postN```
sbml import checks on bounds

This fixes #46.

 - a formula not parsing correctly is downgraded to a warning
 - check that lower and upper bounds are not nan or inf
 - io_test runs fba and chekcs solution
fix #77 removing _b mets in read_legacy_sbml