add --pattern flag to cookbook generator

this will accept environment, application, library, or wrapper as an argument
and it will generate the necessary files for that cookbook pattern
ensure init generator options are available from cli
wrapper cookbooks need a default recipe
rename TYPES constant to PATTERNS
add pkg directory to gitignore
add docs and move `--pattern` flag up to BaseGenerator
Merge pull request #955 from berkshelf/pattern-generator

Add `--type` flag to `berks cookbook` command