Cleanup IObjectStorageMetadataProcessor

* More explicit IObjectStorageMetadataProcessor documentation
* Updated CloudFilesMetadataProcessor to use StringComparer.OrdinalIgnoreCase (fixes #126)
* Updated CloudFilesMetadataProcessor to use string.Length property instead of magic numbers
* Updated CloudFilesMetadataProcessor to use StartsWith instead of Contains
Strongly-typed image types (fixes #129)
Strongly-typed and extensible RebootType (fixes #128)
Strongly-typed ServerState and ImageState (fixes #127)
Merge pull request #131 from sharwell/fix-127,129

Strongly-typed ImageType, ServerState, ImageState
Merge pull request #132 from sharwell/fix-128

Strongly-typed and extensible RebootType (fixes #128)
Merge pull request #134 from sharwell/fix-126

Cleanup IObjectStorageMetadataProcessor