Make a string into a reference, to save a copy
Use a directory in /tmp instead of ~/.config/fish for named pipe path

The home directory may not be able to support named pipes, e.g. if it's
NFS. This puts the file in a secured directory in /tmp
add license for tmux code added in d944add
Replace some std::string with wcstring to reduce copying
Move struct stat checks in configure

Tests for POSIX_C_SOURCE value need to be done before any actual checks
Vim bindings doc: describe modes better and explain some non-vim bindings
update keybindings docs