Add function to compile all script files into a single script file

[HenrikBengtsson]

Add a function startup_compile() to compile all script files into a single script file where the directory and file name filters are translated into if statements. For example, the content of file ~/.bashrc.d/interactive=true/USER!=alice%OR%bob/hello,PAPERSIZE=a4.sh should be injected with the following if statement/wrapper:

## Tags: interactive=true, USER!=alice%OR%bob, PAPERSIZE=a4
if [[ -n "$PS1" && "$USER" != "alice" && "$USER" != "bob" && "$PAPERSIZE" == "a4" ]]; then
  [... file content here ...]
fi

Compiling into a single file may make the overall processing time to go down because fewer files are accessed. It may also help troubleshooting.