Add context version of main functions

[a-urth]

Problem: since main scanning functions use goroutines there is no way to stop them externally if used as library.
Solution: add new function which accept content as first parameters. In main loops of goroutines check for context in select statement and shutdown in case it closed.

[a-urth]

It looks like codacy is running still on first commit and gives error disregard that issue is fixed.