Merge pull request #21 from amalloy/master

Fix warnings
Bump version.
Eliminate reflection.
Add absolute? function

absolute? returns true if given path is absolute.
Add function to join paths
Add find-files function

find-files returns paths of those files beneath a directory that match given
pattern.
Fix typo
Remove join function
Return java.io.Files from find-files
Remove join tests.
added in-any-order flag to contains clause
Added 'exec' method to run a command in the current working directory.
Merge pull request #25 from logosity/master

core_test: added :in-any-order flag to walk tests
Merge pull request #26 from zcaudate/master

Running shell command in cwd
fixed compile error.
Update to lein 2.
Rewrite cwd logic.

Use a dynamic var instead of a mutable thing. We can simulate mutability
by adding a with-mutable-cwd macro that binds *cwd* to itself and then
set! can be used in the body. This is a simple solution.

Closes #24,#22
Merge pull request #27 from ktsujister/fix-compile-error

fixed compile error.
Test against multiple Clojure versions.
Add travis file.