Check directory existence and properly deal with patterned directories

[cpcloud]

closes #151

• asserts that the directory of files must exist when calling resource on it
• patterns like test/*.csv don't iterate over everything in the directory
• provides way to convert a Directory of CSVs into chunks(DataFrame)
• testing on hdfs

[cpcloud]

Alternatively, we could make everything that contains a glob pattern mean chunks

[cpcloud]

pushing to 0.3.3

[llllllllll]

If someone wants to own this please reopen.

[ethanluoyc]

This is still occurring on version 0.5.0 (the latest development version?)
It can be reproduced with the same procedure