How to make a license apply to a whole library?

Question

I'm creating a standard library for a programming language, and I'd like to license each and every single class or function in there under the MIT license, so they're completely FOSS.

All of the files reside in a single directory. Would it be enough to put a LICENSE.txt file in the same directory, containing the MIT license? Do I need to say that the following license applies to all features of the library, or is the library itself considered to be a program?