Make async pragma have same line number as handler

This makes macroutils.nim not show up in compile errors

Example

import mike

"/" -> get:
  unknownSymbol

run()

Before

foo.nim(3, 5) template/generic instantiation of `->` from here
nimbleDir/mike/macroutils.nim(211, 18) template/generic instantiation of `async` from here
foo.nim(4, 3) Error: undeclared identifier: 'unknownSymbol'

After

foo.nim(3, 5) template/generic instantiation of `->` from here
foo.nim(4, 3) Error: undeclared identifier: 'unknownSymbol'

ire4ever1190 / mike

Make async pragma have same line number as handler #25