Add option to return PSCustomObjects

[gabriel-samfira]

This change adds a new option to return PSCustomObjects instead of hashtables. The same option makes powershell-yaml output arrays instead of generic lists.

The new option is called -AsHashtable. By default it's set to true, as not to change the current default and prevent breaking any expectations.

However, you can change the default by setting:

$PSDefaultParameterValues=@{
    "ConvertFrom-Yaml:AsHashtable"=$false
    "cfy:AsHashtable"=$false
}

Anywhere in your script, before calling the powershell-yaml commandlets.

Fixes: #85

[gabriel-samfira]

As mentioned in #85 (comment), using PSCustomObjects will break unserializing YAML that contain case sensitive keys (eg: "a":1 vs "A":2). Dropping this for now.