Merge pull request #102 from skierpage/libs_chapter

Add Programs and Libraries chapter (fixes #101)

src/SUMMARY.md

@@ -59,6 +59,7 @@
     - [Trade-offs]()
         - [Safety and performance]()
         - [Simplicity and expressiveness]()
+    - [Programs and Libraries](./design/programs.md)
     - [Coreutils](./design/coreutils/coreutils.md)
         - [Fail, fail, and fail]()
         - [Simplicty and minimalism]()

src/design/programs_libraries.md

+Programs and Libraries
+======================
+
+Redox can run programs. Some programs are interpreted by a runtime for the program's language, such as a script running in the Ion shell or a Python program. Others are compiled into machine instructions that run on a particular operating system (Redox) and specific hardware (e.g. x86 compatible CPU in 64-bit mode).
+* In Redox compiled binaries use the standard [ELF](https://en.wikipedia.org/wiki/Executable_and_Linkable_Format) ("Executable and Linkable Format") format.
+
+Programs could directly invoke Redox syscalls, but most call library functions that are higher-level and more comfortable to use. You link your program with the libraries it needs.
+* Redox does not support dynamic-link libraries yet *(issue #927)*, so the libraries that a program uses are statically linked into its compiled binary.
+* Most C and C++ programs call functions in a [C standard library](https://en.wikipedia.org/wiki/C_standard_library) ("libc") such as `fopen`
+  * Redox includes a port of the newlib Standard C library. This is how programs such as git can run on Redox. newlib has some POSIX compatibility.
+* Rust programs implicitly or explicitly call functions in the Rust standard library (libstd).
+  * ?? ~~Redox implements a subset of this in libredox~~
+  * The Rust libstd now includes an implementation of its system-dependent parts (such as file access and setting environment variables) for Redox, in `src/libstd/sys/redox`. ?? Most of libstd works in Redox, so many command-line Rust programs can be compiled for Redox.
+
+The Redox ["cookbook" project](https://github.com/redox-os/cookbook) includes recipes for compiling C and Rust projects into Redox binaries.