JSON: fix nullability of JsonArray.FromValues(ReadOnlySpan<string?>) 

Build: fix or add missing README.md files for nuget packages 

Build: import VersionInfo.props in JSON codegen package to pack with … …correct version and metadata

Fdb: fix link to OSX native lib + nuget version range - use proper path to ARM64 OSX dylib - fix nuget package version range so that it can be uploaded to nuget.org

FDB: initial implementation of FqlQuery.EnumerateDirectories() - find all directory subspaces that match a fql query - ex: `/foo/<>/baz` will match `/foo/bar/baz`

Retarget to net5.0 (#109) 

Bump to v6.2.0-preview 

Quick fix of build/test scripts for .NET Core - Can only build with netcoreapp2.2 on linux - add a test.bat/test.sh script - needs to be improved!

Refactored FdbRangeChunk and fixed bug when reading only values - FdbRangeChunk is now a class that implements IReadOnlyList<KeyValuePair<Slice, Slice>> - Added .Keys and .Values pseudo-collections - When reading only the values, we still need to load the first and last key of the chunk to make pagination work (fixes a nullref with multi-page result sets) - Renamed ".Chunk" property into ".Items" to prevent "chunk.Chunk.Length" ugliness in app code. - Old Chunk property is marked obsolete and will be removed soon

Fix ILRepacking of FdbTop