Improve command line interface

[mrocklin]

The into command #69 provides a command line interface to the into function

into myfile.csv myfile.json --delimter ;

Here is a list of possible improvements

• Decrease into import times and latency
• Support keywords anywhere, e.g. into myfile.csv --delimiter ; myfile.json
• Some way to discover keywords based on the file type man into, into csv --help, etc...
• Cleaner error reporting than the current Python stack traces
• Progress bar or at least some reassuring token that promises that progress is being made

@cpcloud and @quasiben came up with most of these ideas. Probably I'm forgetting a few. Please treat this comment as wiki space and add appropriately.

[quasiben]

suggest ';' for delimiter. For example, ', ' is common