add vorburger.exec & zt-exec

Hello @akullpp and awesome-java maintainers,

would you consider adding https://github.com/vorburger/ch.vorburger.exec ? FYI re. "popularity" of vorburger.exec don't look just at the stars on that repo - it's [used really widely indirectly through MariaDB4j](https://github.com/vorburger/MariaDB4j/).

and even the "competition" to (my) vorburger.exec, the https://github.com/zeroturnaround/zt-exec ? ;-) just FYI see also zeroturnaround/zt-exec#25

FYI I'm the same guy from akullpp#465 (and akullpp#653) from a while ago.

Thanks for maintaining this!

README.md

@@ -713,7 +713,9 @@ A curated list of awesome Java frameworks, libraries and software.
 - [Collections](http://commons.apache.org/proper/commons-collections) - Extends or augments the Java Collections Framework.
 - [DBCP](http://commons.apache.org/proper/commons-dbcp) - Database connection pooling services.
 - [Math](http://commons.apache.org/proper/commons-math) - Lightweight, self-contained mathematics and statistics components.
-- [Exec](http://commons.apache.org/proper/commons-exec) - API for dealing with external process execution and environment management in Java.
+- [Exec by Apache Commons] (http://commons.apache.org/proper/commons-exec) - API for dealing with external process execution and environment management in Java.
+- [Exec by Vorburger.ch](https://github.com/vorburger/ch.vorburger.exec) - launch external processes, with significant improvements over Apache Commons Exec.
+- [Exec by ZT](https://github.com/zeroturnaround/zt-exec) - another external process utility
 - [Logging](https://en.wikipedia.org/wiki/Apache_Commons_Logging) Wrapper around a variety of logging API implementations.
 - [OGNL](http://commons.apache.org/proper/commons-ognl) - An Object-Graph Navigation Language.
 - [JCI](http://commons.apache.org/proper/commons-jci) - Java Compiler Interface.