Guard to avoid initialization fail.

[nkoturovic]

Next example resulted in error:

TERM="foo"  # Change $TERM to foo
./demo # executing cppurses demo
# Instead of executing (error prints -> from ncurses::initscr())
Error opening terminal: foo.   # With exit code (1)

Pointing that there is maybe a problem, it might be solved some other (better) way.
Tried to fix it with this patch:

1) If could initialize with $TERM -> okay
2) if not then -> Try to initialize with xterm-256color
3) if both failed then -> Handle error (TODO)

This solution prevents potentially undesired exit(), but on the other hand, hint that there is a problem with $TERM (shown at exit) might be useful for the end user.

Compiled library and tested with demos (everything looks fine).

[a-n-t-h-o-n-y]

Looks good, I'm going to make a few changes so that it throws an exception if the screen cannot be initialized