Create calculate(string) function

[Victorcorcos]

Description ✍️

The the calculate(string) function responsible to evaluate an equation and return it's result

$ ./example
parsec> calculate("1+1")
Result (type: 's'):
ans = "2"
parsec> exit

$ ./example
parsec> number(calculate("1+1"))
Result (type: 'i'):
ans = 2

$ ./example
parsec> calculate("number(calculate(\"1 + 1\")) + 1")
Result (type: 's'):
ans = "3"

[EduardoRSeifert]

Everything seems correct!

[Victorcorcos]

@EduardoRSeifert Can you approve it again?

The merging is still blocked and looks like it is still blocked because I didn't request your review. Now I requested!

[EduardoRSeifert]

LGTM ✔️