Create an initial prosal for supporting native histograms in the text
format. It mainly links to the design doc for ease of comments while we
decide on a path forward. After a proposal from the design doc has some
support the rest of the markdown proposal will be filled out.

Signed-off-by: Chris Marchbanks <[email protected]>

Signed-off-by: Chris Marchbanks <[email protected]>

Signed-off-by: Chris Marchbanks <[email protected]>

Signed-off-by: Chris Marchbanks <[email protected]>

The significant changes are:
1. Add additional examples.
2. Add a proposal for how content negotiation will be done until OM 1.1
   is released.
3. Plural form of arrays in the schema.
4. Added support for multiple exemplars as a non-goal.

Signed-off-by: Chris Marchbanks <[email protected]>

* Tightened up some language of how to tell classic and native
  histograms apart.
* Added that whitespace is not allowed inside of a value.

Signed-off-by: Chris Marchbanks <[email protected]>

Illustrate that ordering matters for this new format to aid parsing.

Signed-off-by: Chris Marchbanks <[email protected]>

Provide a paragraph describing support for multiple exemplars as part of
this proposal. Currently it is left ambiguous if a list of exemplars can
be included on more than native histograms, we can define that
explicitly when writing the new OpenMetrics spec.

Signed-off-by: Chris Marchbanks <[email protected]>

Explicitly state that changing created timestamp semantics and allowing
custom buckets as part of the native histogram structure are not goals
for this proposal.

Signed-off-by: Chris Marchbanks <[email protected]>