Remove nom macros

[cbourjau]

The current code base makes use of nom's macros at many places. The latest release of nom has removed macros entirely. In order to be able to smoothly update nom in the future, it would be nice to replace the existing macros with the corresponding function-versions. We have had some previous discussion on this in #9 and this issue is part of the effort to land the changes of #9 in a piece-meal fashion.