(WIP)

- the `compileFregeTask` has a new optional input called `mainModuleName`. If
it is set, it and only its dependencies will be compiled, otherwise all
`.fr`files in the `mainSourceDir`will be compiled.

- the internal `DependencyFregeTask` is deleted because it was only
used by the vscode plugin and I decided to remove this gradle plugin
as a dependency.

- an example project folder was added to test the plugin manually.

The `replSource` property specifies the frege source file that you want to
load into the repl. It is excluded in the `fregeCompile` task so that
we don't get two java class files (one from `compileFrege` and one
from the fregeRepl `:l` command) that shadow each other on the classpath.

As a result, we can make interactive changes to the `replSource` file and
use the `:r` reload command to see them.

- `depsFregeTask`: only internal use for the vscode plugin to automate the
repl code lens.
- `replFregeTask`: simplified to only print the command to start the repl because
starting and interacting through a console is not gradle's core strength. See
https://github.com/tricktron/frege-gradle-plugin/issues/11.

Increases the max number of test processes, which may reduce the
test execution time.