Tweak grammar and diction

Minor edits: add headers for consistency, fix misspelling, add missing tag.

Added CommonMark support to all description

Grammar nit

Update enum and default type for server variables

More details on 'pattern'

Added required fields

Fixed servers type

Flow to flows

Explicit code over range clarification

Change requestBody default required to false

Added default value to Schema Object's deprecated

clarified `null`

Table formatting fixes

Fix cut and paste error

Change only occurrence of -- to —

Fix two instances of multi-line descriptions leaking from table cells

s/as well as supports/as well as supporting

Resolves #967.

Resolves #954

add missing ":" and quotes in callback object example

Explanation for links confusion, fixes

Updated Examples

[master/2.0] Replace <span>&#124;</span> with \|

Update IMPLEMENTATIONS.md

These projects appear to be at beta stage or better.

added implementations page

# Conflicts:
# versions/3.0.md

Remove Array markers around op.requestBody def.

As discussed [here](https://github.com/googleapis/gnostic/issues/35#issuecomment-290262023)

Add missing quotes to YAML keys.

Small grammar nits

Typo: plain/text → text/plain

Fix the component name regular expression

Fixing link to Parameter Object.

Fix JWT Bearer security JSON sample

Amend wording which might imply property ordering

Renamed ‘Headers’ field to ‘headers’.

Add URL format restriction on termsOfService

updated example issues

Fix text/plain examples in Content Object

Missing capitalisation of 'must'

[v3] Remove extra backtick

Add missing comma in parameter example json

Fix a few missing entries and a broken link in the Table of Contents.

Fix markdown table formatting

Replace <span>&#124;</span> with \|

Bumping version to rc1

As per GitHub's markdown renderer changes

I think this is what was meant here.