Add complete "Makefile" for standard packaging

Also include a ".gitignore" with the derived assets.

---

On the "Makefile", the canonical virtual targets implemented are:

- "all": the default target name when no explicit name is given, or when
  one wants to build more than one target at once, such as:
  `make all check`.  All it builds is the "libsiphash.a" library;
- "check": NOOP, as there are no tests implemented;
- "clean": removes the "*.o", "*.bin" and "libsiphash.a" files, which
  represent 100% of the generated assets;
- "install": uses `$(DESTDIR)`, `$(LIBDIR)`, `$(INCLUDEDIR)` and
  `$(SRCDIR)` to properly place the "libsiphash.a" library, the
  "siphash.h" header and the "siphash.c" source in the correct
  place.  `$(LIBDIR)`, `$(INCLUDEDIR)` and `$(SRCDIR)` are defined based
  on `$(PREFIX)`;
- "uninstall": a perfect mirror of "install", which removes 100% of the
  installed artifacts.

1 files changed, 3 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..155dfbe
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/*.o
+/*.a
+/*.bin