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/ElfInterfaceArm.cpp b/libunwindstack/ElfInterfaceArm.cpp
index bab84cc..66bc51f 100644
--- a/libunwindstack/ElfInterfaceArm.cpp
+++ b/libunwindstack/ElfInterfaceArm.cpp
@@ -17,12 +17,14 @@
 #include <elf.h>
 #include <stdint.h>
 
+#include <unwindstack/Memory.h>
+#include <unwindstack/Regs.h>
+
 #include "ArmExidx.h"
-#include "ElfInterface.h"
 #include "ElfInterfaceArm.h"
 #include "Machine.h"
-#include "Memory.h"
-#include "Regs.h"
+
+namespace unwindstack {
 
 bool ElfInterfaceArm::FindEntry(uint32_t pc, uint64_t* entry_offset) {
   if (start_offset_ == 0 || total_entries_ == 0) {
@@ -127,3 +129,5 @@
   }
   return false;
 }
+
+}  // namespace unwindstack