Make the library usable as a library.

- Add namespace unwindstack everywhere so that it's easier for other
  code to use the library.
- Move some of the header files into include/unwindstack so that they
  can be exposed.
- Modify the headers so that only a limited number need to be exposed.
- Update the tools to use the new headers.
- Add a GetLoadBias() call on the Elf object. This prevents the need
  to get the interface object out of the Elf object.
- Move the GetRelPc() call out of the Reg class, to the Elf class. It's
  not always the case that a Reg object will be around when you want to
  get a relative pc. The tests for this moved to ElfTest.cpp.

Bug: 23762183

Test: Unit tests pass.
Change-Id: Iac609dac1dd90ed83d1a1e24ff2579c96c023bc3
diff --git a/libunwindstack/MapInfo.cpp b/libunwindstack/MapInfo.cpp
index d7b483d..d0e1216 100644
--- a/libunwindstack/MapInfo.cpp
+++ b/libunwindstack/MapInfo.cpp
@@ -20,10 +20,12 @@
 #include <memory>
 #include <string>
 
-#include "Elf.h"
-#include "MapInfo.h"
-#include "Maps.h"
-#include "Memory.h"
+#include <unwindstack/Elf.h>
+#include <unwindstack/MapInfo.h>
+#include <unwindstack/Maps.h>
+#include <unwindstack/Memory.h>
+
+namespace unwindstack {
 
 Memory* MapInfo::CreateMemory(pid_t pid) {
   if (end <= start) {
@@ -86,3 +88,5 @@
   // don't try to reinit the object.
   return elf;
 }
+
+}  // namespace unwindstack