build utilities changes

[madscatt]

1. copy working sassie_2.0 build_utilities files to zazzie
2. consider adding options to renumber indices and resids using the modify pdb fields methods
3. consider adding options to split input pdb files into separate files
4. consider adding options to merge pdb files
5. consider adding options to perform psfgen operations to build structures
6. consider adding options to solvate and ionized structures
7. consider adding options for an overlap check
8. add user vector example(s) to docs
9. draw x-y plane in some of the doc figures
10. add ability to make a fasta file from a full PDB (with selection & comment)