Update README with new automatic path for server.pub

Help text updated.

I just added "You can see message numbers starting client with -N" to the load_photo and the view_photo description.
I've been in trouble because of not knowing how to download files so I think its use-full.
I'm not sure if it's how github works my idea was to Propose this change to the main branch.

Updated rpm with new spec

Basic Debian/Ubuntu package

Adding initial spec to build from source

minor configure.ac simplifications

please add AC_CHECK_LIB([ssl], [function-name]) to configure.ac in the case of failed linkage

fix unused write result in undefined HAVE_EXECINFO_H case

remove printf from signal handlers and reduce configure.ac

use AC_SEARCH_LIB in configure.ac (shorter code)
replace '-lm -lcrypto -lz' by  @LIBS@ in Makefile.in and AC_CHECK_LIB macros in configure.ac
replace NO_BACKTRACE by HAVE_EXECINFO_H

Update interface.c

Fix typo in help command