Changes:
- #1199: Merge latest changes into master
- #1198: Update lib versions
- #1197: Add a commandline option that takes in a metadata version for OpenAPI conversion
- #1195: OpenApiOperation constructor preserve null
- #1192: OpenApiOperation copy constructor - RequestBody null not preserved
- #1190: Bump Microsoft.OpenApi.OData from 1.3.0-preview3 to 1.3.0-preview4
- #1189: Bump Verify.Xunit from 19.11.1 to 19.11.2
- #1188: Bump Microsoft.OpenApi.OData from 1.3.0-preview2 to 1.3.0-preview3
- #1187: Bump Verify.Xunit from 19.11.0 to 19.11.1
- #1186: Bump Verify.Xunit from 19.10.0 to 19.11.0