Add CMake support

[JeffMill]

Seems easy to add. Just include a CMakeLists.txt file:

cmake_minimum_required(VERSION 3.15)
project(figlet LANGUAGES C)

add_executable(figlet crc.c figlet.c getopt.c inflate.c utf8.c zipio.c)

add_executable(chkfont chkfont.c)

with this in place, I was able to build on Windows using:

cmake.exe -DCMAKE_TOOLCHAIN_FILE="$env:VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake" -B figlet

cmake.exe --build figlet --config Release