Update README.md

Remove reference to jit-disable flag
Fixing bug: "Eval with two or more expressions returning undefined".
Added test for it.
Merge pull request #54 from zimbabao/eval-with-two-expressions

Fixing bug: "Eval with two or more expressions returning undefined".
Merge branch 'master' of github.com:maximecb/Higgs into dev-maxime
- Commit before merge