Add semicalc feature to the Calc plugin

[DrorHarari]

Add semicalc (multi-part calculation) feature to the Calc plugin.

For example, writing "10+20+30;*1.3" is equivalent to "(10+20+30)*1.3"

Every semicolon is replaced with the preceding part of the expression, wrapped in parentheses.

Refer to issue https://github.com/Keypirinha/Keypirinha/issues/526