Summary

Solves several memory leaks and SIGSEVs in the client.
Bumps libuast version. Changes include new supported orders for traversing a tree: AnyOrder (we do not give assurances on this order, only that it traverses all the nodes) and ChildrenOrder (to traverse only the immediate children for a node from left to right) and solve memory leaks.
Adds plugins to ease development: sbt-git to take the version to release automatically from the git history and sbt-jni to ease development with JNI.
v2.0.1 did not make it to Maven due to difficulties with build process for macOs and this release supersedes it (#123). This version includes the fix for a linking error with CGO libraries (#119)

Fixed memory leaks

Leaks included in former versions of libuast.
Improves objects management in the native code, taking better care of global references (some of them were not deleted) and improving the caching strategy which could generate memory leaks (#113, #116).
ContextExt did not free native memory.
BblfshClient.decode method used a lot of native memory (due to a nio direct buffer used inside, which uses normal heap space) which was not freed until JVM heap was full and GC (Garbage Collector) was triggered.
If we used a ctx : ContextExt and got a NodeExt or UastIterExt from it and the GC ctx, we could provoke SIGSEVs.

There are some linking problems with older macOS versions (probably 10.11 backwards) due to the need to adjust backward compatibility when compiling libuast (libuast#111)
As noted in previous versions, pending improvements for v2.1.0.