Simplify string handling where possible

[jcline]

Recently made the str class, which leaves adding more functions to make using it simpler. Right now I have to do some painful manipulations to make things usable when interfacing with the curl_interface. Using str_ts everywhere will help with that some, but initialization and concatenation of lots of strings needs to be dead simple.

[jcline]

Need to move urlencoding and filename encoding functions into str.