Support documents and type tags without barfing

These allow Gypsy to "support" the YAML document identifier `---` and type tags. I quote "support" because the way in which it does so is by ignoring them.

Support for the document identifier now allows Gypsy to parse YAML files that look like this:

```yaml
---
config: I am a configuration file
with:
  - option1
  - option2
```

Note, that multiple documents in the same file will probably get concatenated rather than being handled any sort of 'properly'.

Type tagging is now supported, again by ignoring it. YAML files that look like the following will now parse. Obviously no Ruby object will be instantiated and the `!!int` is still parsed as a string because Gypsy does type conversion on lookup.

```yaml
config_name: Welcome
im_an_int: !!int 432
ruby_likes_to_do_this: !ruby/object:ActiveRecord::Model
  id: 1
  name: john
```