Version 1.8.1

• Fixed load_env_levels() and load_argv_levels() #1680 (thanks @Tridacnid ).
• Fixed stdout sink that produced extra carriage returns on Windows #1675 (thanks @chris-t-w ).
• Fixed msvc_sink including windows.h #1667 (thanks @Ryan-rsm-McKenzie).
• Fixed stopwatch's clock to use chrono::steady_clock #1676 (thanks @SuperWig).
• Added support for Rcpp (R cpp compiler) #1685 (thanks @eddelbuettel).