Way to add directories into load/library path

I know this is not relevant yet, but I thought I'd open an issue for when it is.

Most Scheme implementations have way to add a directory into "load path", path were load procedure tries to find files and import tries to find libraries.

So if you have main.scm:
```
(import (scheme base)
(foo bar))

(baz)
```

Running it with `lips -A mylibraries main.scm` would add ./mylibraries into library search path and hopefully foo/bar.sld is there and it is found. I used -A as example as it is mentioned in SRFI 138: Compiling Scheme programs to executables. And it is also part of the reasion I'm opening this issue now, while -A, -I and -D are still available. 😄

Start by tracing how the lips CLI currently handles -A, -I, and -D, then inspect the load and import resolution paths. Use main.scm with `(foo bar)` and a foo/bar.sld under mylibraries as the acceptance example; done means the requested directory is searched for libraries and loaded files.

Written by the indexing model from the issue text.