[configs/alter] December update

* Remove package:
  * deadbeef-mpris-plugin - doesn't work fine any more
  * screen - ship a setuid binary by default
* Add package:
  * mosh
  * indent - formatting C code
  * splint - check the code mistakes in C code
  * rdesktop - client for Windows Remote Desktop Services
  * rar - create RAR archives
  * autogen - required to build some pkg
  * gperf - required to build some pkg
  * help2man - helper utility to generate manual page from `--help` output
  * diffstat - tool to histogram of diff changes
  * xmlto - required to build some pkg
  * intltool - required to build some pkg
  * burp - AUR uploader
  * expac - ALPM database extraction tool
  * doxygen - documentation system for C++, C, Java, IDL and PHP
  * gcc-ada - ADA frontend of gcc
  * gcc-fortran - Fortran frontend of gcc
  * linux-docs - Linux documentation
  * valgrind - tool to help find memory-management problems in programs
  * mlocate - provides 'locate'
  * xarchiver - simple GTK+ frontend to many CLI archivers
* Update the Offline installation guide