update zlib to 1.2.8 and OpenSSL to 1.0.1j

zlib 1.2.4 is too old and OpenSSL 0.9.8n has multiple
security vulnerabilities in it, so update it to the
latest versions. Instead of compiling it on the fly,
pre-compiled versions are included for both libraries.
fix compilation with updated zlib and OpenSSL
remove embedded libssh and update to libssh 0.6.4

This fixes multiple bugs reported in Notepad++ and NppFTP:
http://sourceforge.net/p/nppftp/bugs/71/
http://sourceforge.net/p/notepad-plus/bugs/5031/
http://sourceforge.net/p/notepad-plus/bugs/5045/
fix compilation issues with updated libssh
add README with build instructions
update version to 0.26