Missing comments for some firebase-document attributes/methods

[phidias51]

Missing comments for the following firebase-document attributes:

• isNew
• app
• appName
• db
• ref
• path (the description says "N.B. path is case sensitive" but doesn't explain what 'N.B.' means", abbreviations should be spelled out before use)
• zeroValue

Comments should also indicate which attributes are required.

The following methods & method parameter comments are missing:

• destroy()
• getStoredValue(path)
• memoryPathToStoragePath(path)
• reset()
• setStoredValue(path, value)
• storagePathToMemoryPath(storagePath)

[hedcet]

isNew & zeroValue r getter so zeroValue can't set