* Rewrite FirestoreEncoderTests using assertThat
* Throw invalidValue for use of invalid top-level values
* Provide an message for not supported errors
* working serverTimestamp
* working FieldValue. Still need: document ref and ability to Eq of FieldValue
* DocumentReference implemented and testing works
* clean up header search path
* improving FieldValue enum comments
* run through formatting
* addressing comments
* formatted with swiftformat 0.35.7
* add missing bool->BOOL change
* undo unintended swift version change
* remove unwanted proj file change
Sheikh Bayazid