Built `bind` method for sites, downloads and datasets to join multiple search results.
- not implemented: search and warn for duplicates
- Made sure all datasets had names assigned in the dataset_list
- rebuilt package.
Merged @gavinsimpson's weird indents and didn't want to fix it back.

Merge remote-tracking branch 'upstream/master'

Conflicts:
	R/get_dataset.R
Merge pull request #155 from SimonGoring/master

Added the bind method and merged @gavinsimpson's upstream pull #154