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/DwarfMemory.cpp b/libunwindstack/DwarfMemory.cpp
index a984fc6..b6e0412 100644
--- a/libunwindstack/DwarfMemory.cpp
+++ b/libunwindstack/DwarfMemory.cpp
@@ -18,10 +18,13 @@
 
 #include <string>
 
+#include <unwindstack/DwarfMemory.h>
+#include <unwindstack/Memory.h>
+
 #include "Check.h"
 #include "DwarfEncoding.h"
-#include "DwarfMemory.h"
-#include "Memory.h"
+
+namespace unwindstack {
 
 bool DwarfMemory::ReadBytes(void* dst, size_t num_bytes) {
   if (!memory_->Read(cur_offset_, dst, num_bytes)) {
@@ -246,3 +249,5 @@
 
 template bool DwarfMemory::ReadEncodedValue<uint32_t>(uint8_t, uint64_t*);
 template bool DwarfMemory::ReadEncodedValue<uint64_t>(uint8_t, uint64_t*);
+
+}  // namespace unwindstack