Add module READMEs, .gitignore, and remove Bin/ from tracking

Add README.md for each library module documenting API, platform
backends, and usage. Add .gitignore for build artifacts. Remove
pre-built binaries from version control.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

libsst-atomic/README.md

@@ -0,0 +1,33 @@
+# libsst-atomic
+
+Cross-platform atomic operations implemented in hand-written assembly for
+lock-free programming.
+
+## API
+
+All functions operate on `volatile int*` or `volatile void**`:
+
+- **Add / AddPtr** -- atomic add (with optional return of new value)
+- **And / Or / Xor / Not** -- atomic bitwise ops (with optional return)
+- **Exchange / ExchangePtr** -- swap value, return old
+- **ExchangeAdd / ExchangeAddPtr** -- add, return old value
+- **CAS / CASPtr** -- compare-and-swap, return old value
+- **LoadAcquire / LoadAcquirePtr** -- load with acquire semantics
+- **StoreRelease / StoreReleasePtr** -- store with release semantics
+
+## Architecture support
+
+Each backend is a standalone `.asm` file:
+
+| File | Architecture | ABI |
+|---|---|---|
+| SST_Atomic_x86.asm | x86 (32-bit) | cdecl |
+| SST_Atomic_x86-64.asm | x86-64 | System V |
+| SST_Atomic_x86-64-win64.asm | x86-64 | Microsoft x64 |
+| SST_Atomic_arm.asm | ARMv6+ | ARM EABI |
+| SST_Atomic_ia64.asm | Itanium | IA-64 |
+| SST_Atomic_mips.asm | MIPS32R2+ | o32 |
+| SST_Atomic_mips64.asm | MIPS64R2+ | n64 |
+| SST_Atomic_ppc.asm | PowerPC 32 | SysV |
+| SST_Atomic_sparc.asm | SPARCv9 32 | SPARC |
+| SST_Atomic_sparc64.asm | SPARCv9 64 | SPARC |