detect .tsv file extension
add --tsv command-line option

Tab-separated tables (.tsv) are really common in unix-based informatics
pipelines. Adding a --tsv cli option makes it much simpler to pipe in and out
tab-separated data.
test for csv and tsv import from stdin
Merge https://github.com/maxogden/dat

Resolve conflicts due to basing this on another PR.

Conflicts:
	bin/import.js
	lib/commands.js
	test/tests/cli.js
Merge pull request #232 from ekg/master

add --tsv import/export option to cli