Update readme
Remove unused import
Add APISpec#add_path
Fix implementation of add_path
Refactor add_path; handle kwargs in Path constructor
Further refactoring; just pass operation dict to Path constructor
Generalize casing corrections
Refactor as dict comprehension and add docs

also, add tests
Handle nested field in field2property
Use ref if available on nested field
Convert Nested lists to swagger specs
Merge branch 'paths' into dev