Bump to 0.2.0-SNAPSHOT; upgrade dependencies.
remove verbose namespace.
refactor the whole implementation.

- Versions are no longer given as tupels but as a map of
  `:version-string` and `:version`.
- Throwables are returned where possible, enabling parallelization.
add tests.
update README.md
update README.md
move 'distinct' to core code.
update README.md
fix ':form' in artifact map.
make 'read-artifact' part of public API.
convert ':url' -> ':uri' and ':password' -> ':passphrase'.
add TravisCI SVG badge.
add tests for other core functions.
add TTL/LRU caching to loaders. (closes #3).
Version 0.2.0
Back to SNAPSHOT.