JDK 13 (#107)

* Test build against JDK 13

* Replace badge with JDK compatibility indicators

* Change README to markdown

* Fix links in README

.github/workflows/maven-build.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: [ 8, 11 ]
+        java: [ 8, 11, 13 ]
     steps:
       - uses: actions/checkout@v2
       - name: Set up JDK ${{ matrix.java }}

README.md

@@ -0,0 +1,13 @@
+# GitDB - Git as a (Stupid) NoSQL Database
+
+An experiment in working with a bare Git repo to do something that probably
+shouldn't be used in production.
+
+![Java 8](https://img.shields.io/badge/Java-8-success "Compatible with Java 8")
+![Java 11](https://img.shields.io/badge/Java-11-success "Compatible with Java 11")
+![Java 13](https://img.shields.io/badge/Java-13-success "Compatible with Java 13")
+![Java 14](https://img.shields.io/badge/Java-14-important "Unresolved Issues with Java 14")
+
+Inspired by the [presentation](https://www.youtube.com/watch?v=nPPlyjMlQ34)
+and [blog post](https://www.kenneth-truyers.net/2016/10/13/git-nosql-database/)
+by Kenneth Truyers.

README.org

@@ -1,10 +0,0 @@
-* GitDB - Git as a (Stupid) NoSQL Database
-
-  An experiment in working with a bare Git repo to do something that
-  probably shouldn't be used in production.
-
-  [[https://oss.sonatype.org/content/repositories/releases/net/kemitix/gitdb][file:https://img.shields.io/nexus/r/https/oss.sonatype.org/net.kemitix/gitdb.svg?style=for-the-badge]]
-  [[https://search.maven.org/#search%7Cga%7C1%7Cg%3A%22net.kemitix%22%20AND%20a%3A%22gitdb%22][file:https://img.shields.io/maven-central/v/net.kemitix/gitdb.svg?style=for-the-badge]]
-  [[http://i.jpeek.org/net.kemitix/gitdb/index.html][file:http://i.jpeek.org/net.kemitix/gitdb/badge.svg]]
-
-  Inspired by the [[https://www.youtube.com/watch?v=nPPlyjMlQ34][presentation]] and [[https://www.kenneth-truyers.net/2016/10/13/git-nosql-database/][blog post]] by Kenneth Truyers.