Async, Ktor, Batch Requests, Minor changes

Basically I'm stabilizing the changes from the previous pre-releases. Minor changes:

• Small adjustment in the getUUIDsByNames function, as invalid user names are now rejected by the server
• Regression test for that
• bumped kotlin, kotlin-serialization and klock to new versions to support Kotlin 1.4.10 and stable serialization branch.

jitpack compatibility

this pre-release is compatible with jitpack.io

Prerelease 2.0

This is a pre-release of the 2.0 version of the library. As the version number indicates, it is a breaking change.

The major changes in short:

• switched http client engine to ktor. This enables you to use any engine you like by including it as a dependency.
• the API is fully asynchronous
• the API is multiplatform-ready for JS and JVM. Native, Android and iOS are planned and shouldn't be too hard to add.
• the status API is finally implemented
• uploading skins by file is currently unsupported, because of the multiplatform support. Will re-add it later
• added a batch-request for user profiles

MojangClient fully implemented

The MojangClient API is now fully implemented.
Still missing status API though.

Session now holds UUID by default

• Session now holds UUID by default
• Slight adjustments to JavaDoc (still not perfect)
• Slight adjustments to test cases

Nidhogg 1.1 PRE

Merge remote-tracking branch 'origin/master'

First Release

All basic Yggdrasil resources are accessible, Data objects for credentials and session are provided