Version 1.6.7

version bump

fix for unicode issue with 2.7.13

version bump for release

Minor patch but we ran out of version numbers

* cplex fixes

Fixed issue with

- cbc path on osX
- gplk scientific notation in solution files

Fixed ** issues with readsol_LP

added __iadd__ and __isub__ for LpAffineExpression
deletes mps files properly
fixes calls to root logger