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/DwarfDebugFrame.h b/libunwindstack/DwarfDebugFrame.h
index 320368c..6a6178e 100644
--- a/libunwindstack/DwarfDebugFrame.h
+++ b/libunwindstack/DwarfDebugFrame.h
@@ -21,7 +21,9 @@
 
 #include <vector>
 
-#include "DwarfSection.h"
+#include <unwindstack/DwarfSection.h>
+
+namespace unwindstack {
 
 template <typename AddressType>
 class DwarfDebugFrame : public DwarfSectionImpl<AddressType> {
@@ -73,4 +75,6 @@
   std::vector<FdeInfo> fdes_;
 };
 
+}  // namespace unwindstack
+
 #endif  // _LIBUNWINDSTACK_DWARF_DEBUG_FRAME_H