RFC 0003, 0007 updates (Metrics measure type, metrics handle specific…

…ation), RFC 0004 (configurable aggregation) deleted (open-telemetry#29)

* Updates to 0003 following work session 8/21/2019

* Update date

* Feedback applied

* Feedback applied

* Remove handle specification, will create another RFC

* More typing

* Add metrics handles RFC

* Rename 0000

* Remove 0004

* Add an open question from python PR87

* Add an open question about RecordBatch

* Clarify the open questions

* Name NonNegative and NonDescending options

* Clarify the Measurement unit for RecordBatch

* Add issues addressed

* Linkify

* Linkify

* Format

* Address option names and default settings

* Answer questions

* Spelling

* Use 0007

* Refer to 0008

* Take suggestion