doc: Man page cleanup

Simlify example sections.
Remove un-needed .LP after section start.
Insert empty line before section start.
doc: Follow xrdp- rename

sesman and sesrun were prefixed with xrdp- a long time ago.
Update the manual pags to follow that change as well.
doc: Update xrdp.ini options

Update General section.
Document Logging section.
Document Channels section.
doc: xrdp-sesadmin manual page

Add a manual page for xrdp-sessadmin.
doc: xrdp-dis manual page

Add a manual page for xrdp-dis, which is used to disconnect the RDP
connection but otherwise keep the session running.
doc: xrdp-xcon manual page

Add a manual page for xrdp-xcon, which is currently not installed, since
xrdp-xcon is not installed.
doc: xrdp-keygen manual page

Add updated manual page from Debian project.
doc: xrdp-genkeymap manual page

Add manual page for key map generation utility.
doc: xrdp-sessvc manual page

Add manual page for internally called xrdp-sessvc.

The program should probably be moved to /usr/lib/xrdp/ as it's only
called internally.
doc: xrdp-chansrv manual page

Add manual page for internally forked channel server.