doca - Create an option for schema glob

Currently the `**/*.json` glob for finding schemas is not changeable. (hard coded).

My schema project has the following layout

```
/schemas/
/foo/something-special.schema.json
/foo/something-speacial-sample-data-1.json
/foo'something-speacial-sample-data-1.json
```
I need to be able to glob on just `**/*.schema.json`

for example

```
doca init -g "**/*.schema.json" -o docs
```

This is my attempt...
https://github.com/rbuckland/json-schema-tools/tree/feature/doca-glob-option