Fix Tx.Buckets() sort order.

@tv42 reported an issue with bucket names returning incorrectly. Not sure if
this fixes the issue but it is necessary anyway.
Skip long-running tests with go test -short
Merge pull request #66 from tv42/testing-short

Skip long-running tests with go test -short
Fix Bucket.ForEach() comment.
Merge pull request #65 from benbjohnson/fix-tx-buckets-sort-order

Fix Tx.Buckets() sort order.
Remove ease-of-use functions from the DB type.

Functions such as DB.Put(), DB.Get(), and DB.Delete() were originally
added to be easy to use, however, after implementing Bolt in multiple
projects I have found these ease-of-use functions useless. Nearly
every use case requires multiple calls in a single transaction.

Using the DB ease of use functions turned out to be an antipattern.
Merge pull request #68 from benbjohnson/remove-db-functions

Remove ease-of-use functions from the DB type.
Fix db.munmap() to return an error.

Changes munmap to return an error and the DB now implements io.Closer.
I also removed all the OS and Syscall mocking because it's causing issues.
Corrupt file tests need to be recreated but directly using the file system
instead.
Merge pull request #71 from benbjohnson/munmap-fix

Fix db.munmap() to return an error.
Add 'bolt get'.
Add 'bolt keys'.
Add 'bolt pages'.
Add 'bolt set'.
Add 'bolt buckets'.
Fix print.
Merge pull request #74 from benbjohnson/cli

CLI