Merge pull request #70 from cboettig/master

use updated location for rstudio docker image
Update docs
Tweaks to freeze/thaw
Add space after waiting message
Use create instead of new. Closes #73
modified cli_tools fxn a bit, added within do_system fxn to check for scp and ssh #72
improved cli_tools code, #72
rbuildignore update
Add link to sizes function
Make it possible to specify keys by name
Improve droplet print method
Improve create documentation
Warn if no ssh_keys supplied
Default to using all ssh_keys in account
Extract standardise keys into own function
Remove old install scripts
Use inheritParams instead of template
Remove old roxygen templates
Remove unneeded ignores. Tighten up regexps
Fix broken link