Finished up the parts related to string edit distance.

  - reworded my last paragraph
  - added a couple paragraphs of documentation to the actual code
  - the text still needs editing though!
Reorganized .gitignore

  - broke it into sections
  - added autogenerated LaTeX garbage
  - added a section for one-off specific files
Started working on the actual Tree Edit Distance section.

  - began describing the Zhang-Shasha algorithm
  - generated diagrams for each of the tree edit operations