Internally LIBRESSL_SKIP_INSTALL, if not set becomes ENABLE_LIBRESSL_INSTALL so this by default is enabled. defining LIBRESSL_SKIP_INSTALL before hand will disable all install() rules.
This is useful if another project includes and links to this statically.
I chose to add a prefix to avoid potential name collision because the options are cached globally.
If the installation is skipped, maybe it should also disable building apps? I didn't do that.
- modify structure of CMakeLists.txt under apps/
* move apps/CMakeLists.txt to apps/openssl/ since this is for openssl build
* create new apps/nc/CMakeLists.txt for nc build
* modify apps/CMakeLists.txt just add_subdirectory()
- add checking and compile of arc4random_uniform()
- add installing man files, openssl.1 and nc.1
