These changes are to improve the experience for publishing these proposals.
One change should be carefully reviewed to ensure I didn't introduce any technical errors:
I translated the binary literals grammar into ANTLR to match all other specs and proposals. See changes in proposals/csharp-7.0/binary-literals.md
Other changes are:
1. Use consistent ATX headers, with one H1 per proposal.
1. use `csharp` as language identifier in code snippets
1. Use relative links to other markdown from the dotnet/csharplang repo. That way, when published on docs.microsoft.com, the links will resolve to the publsihed articles on the same site. (Links to content not being published are not modified.)
1. spelling / capitalization found by the lint tool.
