Fix evals and other minor changes

[solivella]

1. Replace non-standard evals with direct internal function calls
2. Replace arg and arg type in get_census_data (counties --> county.list) to list of county names, allowing state-specific county name vectors
3. Unexport internal funs; only export three main functions
4. Eliminate unnecessary dependency on stringr and devtools
5. Don't ask for census related things if surname.only==TRUE
6. Change use_counties to use.counties to match style of other args

[1beb]

@solivella A small update should be added. You've wrapped the note about race init in control$verbose, however, what if no one defines control.