add experimental module support

[eiiches]

This PR adds an experimental Module support to jackson-jq.

To use this feature, users need to set ModuleLoader to the scope (by default all import fails).

rootScope.setModuleLoader(new ChainedModuleLoader(new ModuleLoader[] {
	BuiltinModuleLoader.getInstance(), // enable loading modules via ServiceLoader
	new FileSystemModuleLoader(rootScope, Versions.JQ_1_6,
		FileSystems.getDefault().getPath("").toAbsolutePath(), // enable loading modules from current directory,
		Paths.get(Scope.class.getClassLoader().getResource("classpath_modules").toURI())), // and from Java classpath
}));

Todo:

• Implement FileSystemModuleLoader
  • We should also be able to use Java classpath instead of the actual file system
  • We must prevent directory traversals
  • Support altering search path in the import directive: import "foo" as foo {search: "./"}
  • Cache loaded modules
  • Forbid recursive imports
• module directive
• modulemeta/0
• Add Map<String, Module> BuiltinModuleLoader#loadAllModules() method
  • Hopefully Quarkus extension can make use of this method to enumerate and serialize built-in Modules
• NullModuleLoader should be in the internal package
• Add tests

resolves #43

[eiiches]

It might be useful if Java classes (limited to ones that are allowed in configuration) can be directly imported into jq.

import "java.lang.Math" as jmath;

jmath::sqrt(3)

I'm not gonna implement this in this PR, but I believe this could be done by writing a ModuleLoader that reflectively generates Function instances from Java methods.

[eiiches]

modulemeta/0 will not be implemented in this PR because I couldn't figure out what it does or how to use it.

$ cat foo.jq
module {"name": "foo"};
def one: 1;
$ jq-1.6 -n 'import "foo" as foo; foo::one, ("foo" | modulemeta)'
1
jq: error (at <unknown>): module not found: foo