implemented parser based on a Node protocol.
adjust parser tests; fix discovered bugs.
update .gitignore.
add coercion, tests and bugfixes.
remove now-unused tests.
reimplement first few zipper functions.
make coercion work by requiring protocol implementations.
let FormsNode produce its only children (if applicable).
move reader/writer functions to zipper base ns.
add tests for whitespace/base zipper fns.
add tests for zipper find operations.
add removal utilities.
add zipper movement tests.
add insert zipper functions.
fix filename.
add removal functions.
add edit/replace functions.
add subedit/scoped edit functions.
add seq zipper functions.
add prefix/suffix; fix transform tests.