Change math engine to libqalculate and add new functions
Replaces knumber with libqalculate and brings the following key benefits:
- New functions
- Displays fraction format for approximate numbers
- Unit conversion is available within calculations
- Reduced code to maintain
- Fault-tolerant parsing of strings and brings back implicit multiply
- And much much more qalculate.github.io/
Closes #12 (closed)
Edited by Michael Lang