Prepend `X-` to default context tags. (TileDB-Inc#1410)

Also add the library version as a default tag.

Merge pull request TileDB-Inc#1397 from TileDB-Inc/ttd/backport-schema-h

Backport fix to 1.6.3

Update HISTORY.md and version numbers for 1.6.2.

Add HADOOP_VERSION variable, and bump to 3.1.2 to try to fix download…

… failure

(cherry picked from commit 56ec1b7)

Update HISTORY.md and doc links for 1.6.0.

Update version numbers to 1.5.1

Update HISTORY.md and example links for 1.5.0 release.

Bump version to 1.4.2

Bump version numbers to 1.4.1

Merge pull request TileDB-Inc#1026 from TileDB-Inc/ttd/update-go-doc-…

…link

Update Go documentation link to use v0.2.0 tag.