Merge pull request #14 from noamross/master

Added ability to filter cr_search by record type
regenerated man file for cr_search with type arg, bumped date
Merge pull request #15 from noamross/master

Error handling for invalid DOIs in cr_cn()
tweaked error text try returns in cr_cn to return simple character string, #15
Retain failed DOI in error messages.

Merge remote-tracking branch 'upstream/master'

Conflicts:
	R/cr_cn.r