Pyyeti

This update is all about enhancing and fixing a bug in the Nastran tools. The bug was that pyYeti did not properly handle upstream superelements that did not connect all 6 DOF for all boundary grids. This can happen for superelements brought in via EXTSEOUT.

Also enhanced the PARAM,POST,-1 op2 file reader (the pyyeti.nastran.op2.rdpostop2 function) to return more information organized by superelement.

Bug fix for the op2 reader (now can handle more than 32 superelements).
Update the n2p.find_xyz_triples routine to be more robust and added the "tol" parameter.
Update the README.md file to update the install notes

Minor update; primarily made the matplotlib import in setup.py optional by using try/except.
Also improved testing for the new "asm2uset" routine.

Primarily minor documentation updates and bug fixes.
Enhanced the nastran.bulk.rdseconct routine to accept more card formats.

- update uset usage in cb.cbcheck and cb.mk_net_drms (can include non bset DOF)
- attempt to prevent datacursor.DataCursor._setup_annotations() (scatter) from resetting axes limits

Add pyyeti.nastran.bulk.asm2uset -- a more robust version of "bulk2uset" specifically for Nastran .asm files.
Add rdspoints, rdseconct in the same "bulk" module.
Bug fixes and documentation updates