78 refactor

[Robinlovelace]

• Shift route variable to argument
• Add placeholder docs
• Add working example for json2sf_cs2
• Add checks
• Get journey working with json2sf_cs2
• Replace json2sf_cs with faster fun
• Document
• Fix bind_sf
• id has default value
• Update examples, no errors
• Minor fixes
• Rm sfheaders
• Keep fewer cols
• Add cols_to_keep to batch()

[Robinlovelace]

Please take a look when you get a chance @mem48 also, I've switched to using your functions and removed the old ones, allowing us to remove ~500 lines :tada:

[Robinlovelace]

This is much better, lots of improvements, big and small. So merging! Post-merge review welcome.