Common Denominator [FEATURE]

[andrew-murdza]

Implement these rules

• \frac{a}{b}+\frac{c}{d}->\frac{ad+bc}{bd}
• \frac{a}{b}-\frac{c}{d}->\frac{ad-bc}{bd}
• -\frac{a}{b}-\frac{c}{d}->\frac{-ad-bc}{bd}
• \frac{a}{b}+\frac{c}{b}->\frac{a+c}{b}
• \frac{a}{b}-\frac{c}{b}->\frac{a-c}{b}
• \frac{a}{b}+c->\frac{a+bc}{b}
• -\frac{a}{b}+c->\frac{-a+bc}{b}