textproc/pychm: fix runtime
- fix missing symbol _get_leaf_node_offset which causes chm2pdf to exit
- pass maintainership to submitter
- bump PORTREVISION
While here, limit python version to 2.x, since it doesn't build with 3.x and
convert to autoplist.
PR: 201351
Submitted by: Carlos Jacobo Puga Medina <cpm@fbsd.es>