CMake addition request

[robiwano]

With the following addition it is extremely easy to add cereal to CMake based projects:

ADD_LIBRARY(cereal INTERFACE)

TARGET_INCLUDE_DIRECTORIES(
cereal
INTERFACE include
)

When a project uses TARGET_LINK_LIBRARIES(target ... cereal ... ), include paths will be set automatically for the given target.

[AzothAmmo]

Do you think you can create a pull request for this?

[robiwano]

Don't know currently how that works, just recently took the great "git plunge" :) Shall see what I can do.

[tamaskenez]

I continued this issue in #254