added static library target

[camradeling]

With this tiny change one can easily integrate this repo as a submodule without need to build it complete and modifying source lists.

Example of top level repo CMakeLists.txt:

include_directories(
./binapi/include
)

add_subdirectory(binapi EXCLUDE_FROM_ALL)

add_executable(
${PROJECT_NAME}
#
main.cpp
)

add_dependencies(${PROJECT_NAME}
binapi_static
)

target_link_directories(${PROJECT_NAME}
PUBLIC
${CMAKE_BINARY_DIR}/binapi
)

target_link_libraries(${PROJECT_NAME}
libbinapi_static.a
z
crypto
ssl
pthread
)