Addresses issue #432 by adding a `noArrayIndent` option to optionally not add an extra level of indentation to array elements.

When `noArrayIndent` option is set to `false` (or not provided), output is:
```
array:
  - a
  - b
  - c
```

When `noArrayIndent` option is set to `true`, output is:
```
array:
- a
- b
- c
```

This helps avoid diffs when parsing, modifying, and generating valid yaml that does *not* use extra indentation for arrays.

fix #475

... when object with executable toString() property is used as a map key

Fix possible code execution in (already unsafe) load()