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/ElfInterface.cpp b/libunwindstack/ElfInterface.cpp
index 7d38ee0..75abc85 100644
--- a/libunwindstack/ElfInterface.cpp
+++ b/libunwindstack/ElfInterface.cpp
@@ -24,15 +24,18 @@
 #include <Xz.h>
 #include <XzCrc64.h>
 
+#include <unwindstack/DwarfSection.h>
+#include <unwindstack/ElfInterface.h>
+#include <unwindstack/Log.h>
+#include <unwindstack/Memory.h>
+#include <unwindstack/Regs.h>
+
 #include "DwarfDebugFrame.h"
 #include "DwarfEhFrame.h"
-#include "DwarfSection.h"
-#include "ElfInterface.h"
-#include "Log.h"
-#include "Memory.h"
-#include "Regs.h"
 #include "Symbols.h"
 
+namespace unwindstack {
+
 ElfInterface::~ElfInterface() {
   for (auto symbol : symbols_) {
     delete symbol;
@@ -387,3 +390,5 @@
                                                                    uint64_t*);
 template bool ElfInterface::GetFunctionNameWithTemplate<Elf64_Sym>(uint64_t, std::string*,
                                                                    uint64_t*);
+
+}  // namespace unwindstack