Parse simple equation into terms

[sjelatex]

The current version (v1.2) can only handle very simple equation with no fractions and parenthesis e.g. equations like 2a+b-3c-1. The upcoming version in the branch version2-draft will support fractional calculus, and been updated to handle fractions e.g. 2/n+b-3c/2-1/2. But the algorithm can still not support parenthesis. This will be ideal to because terms like 1/(m+n) may not be handled correctly. Or terms like (m+n)/2 is definitely not handled correctly as m/2+n/2.