Various code cleanup; expert-mode toggle; throbber cleanup
* Added newuser.c
* Implemented (basic) login/auth
* Rough-draft of newuser process
* Restructuring of many string references from S_* to S_MSG_*
* Added prompt*() versions of input*()
* promptp() - for passwords/protected input
* Some input code cleanup
* plugin_del actually does.  Or, should, anyway...
* Better file IO error handling
* Added auto-sysop-flag for user number 1; serious auth bug when no login username
Adding data/ to ignored directories
Merge branch 'master' of https://github.com/mholger/terminus