better cache sizing
kill superfluous warning
rename repo->root to repo->pool
allow overriding pool with --pool/-p flag
make symlinks across when root != pool directory
expand filematching logic for -U

Arguments to -U are now handled more intelligently.

If its a full path, attempt to load that package. Otherwise scan
through the repo's directory looking for matches:

- If there's a match against a package's filename, load that package
- If there's a match against a package's name, load that package
- If a glob against pkgname-pkgver succeeds, load that package
intelligently handle arch, add -a/--arch

It doesn't make sense for a repo to mix architectures. By default only
load packages with an architecture that matches the machine's arch. Add
a flag to allow overriding arch (useful when cross compiling).
handle REPO_NEW in repo_write
search for repo signature in root directory