Expose position information somehow

[emberian]

In PLY, the lineno, lexpos, linespan, and lexspan methods of YaccProduction (the type of p) allow recovering position information from parsed terminals and non-terminals. This is often important in robust parsers, for error reporting during or after parsing. easyply doesn't yet support this, but it should.

[emberian]

One design: set those corresponding attributes on the named terms before passing them, in the wrapper function. Unfortunately, this might conflict with already-defined attributes. To work around that, it would check if hasattr(o, 'easyply_name_map'), and if so look up lineno etc in that to get the actual name for setattr.

[wa-dev]

It would it nice to provide a list of attributes to copy in addition to lineno, lexpos, linespan, and lexspan. For instance, I normally attach a filename attribute to my tokens when parsing files with multiple includes.

[wa-dev]

This functionality can be implemented with #7

[wa-dev]

In #8 an additional function has been added to the api (easyply.location) to track term position.