Add trivial example of using Rcpp in modules

Dynamically compile a source file upon `import`ing a module.
Add example of compiling dynamic library

Unlike the trivial Rcpp example, this caches the compiled module.
Add documentation for code compilation
Add compiled documentation
Merge branch 'rcpp-example' into develop
Fix link to install file
Add Rcpp link
Merge branch 'rcpp-example' into develop
… and *compile* everything.
Merge branch 'rcpp-example' into develop
Test that module base paths reflect script path
Remove bogus test assertion
Improve error reporting
Use correct script path instead of current dir

`module_base_path` and `import_search_path` now rely on the current
script/module path instead of the current working directory. This is an
attempt to fix #15.
Merge branch 'issue-15' into develop
Remove required `__init__.r` files in supermodules

FIx #16 modulo the need to check for module init files more smartly
(which needs fixing anyway with relative import paths), and the
amendment of test cases.
Add test for #18 and #24
Make imports with leading dot always relative

Fix #18.
Make imports absolute by default

Reorder the import search path to make imports non-local by default.
This fixes #24.
Don’t change directory to imported source file

Remove `chdir` argument to `source` in `import`, which is logically not
necessary any more, and was never desired.