Add notes about modularity

Author: fragglet

README.md

@@ -5,6 +5,11 @@ comparison to other modern programming languages. This is a collection of
 common computer science data structures and algorithms which may be used in C
 projects.
 
+The project is structured in a modular way, such that it is possible to
+trivially copy any module (pair of `.c` and `.h` files) into a project without
+dealing with the usual hassle of library dependencies. However, the project
+does also build as a library named `libcalg` if that's what you want.
+
 The code is licensed under the [ISC license](COPYING.md), a permissive license
 that is functionally identical to the MIT or BSD licenses. As such, it may
 legitimately be reused in any project, whether proprietary or open source.

STYLE.md

@@ -72,3 +72,10 @@ All public interfaces must be documented using
  */
 unsigned int hash_table_num_entries(HashTable *hash_table);
 ```
+
+## Modularity
+
+The project is structured in a modular way, such that each module (`.c` and
+`.h` file) is independent of the others. The idea is that anyone should be able
+to use any file in an "off the shelf" way by trivially copying those two files
+into their project.