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/tests/LogFake.cpp b/libunwindstack/tests/LogFake.cpp
index 411594a..537ccaf 100644
--- a/libunwindstack/tests/LogFake.cpp
+++ b/libunwindstack/tests/LogFake.cpp
@@ -25,7 +25,6 @@
 #include "LogFake.h"
 
 // Forward declarations.
-class Backtrace;
 struct EventTagMap;
 struct AndroidLogEntry;
 
@@ -33,6 +32,8 @@
 
 std::string g_fake_log_print;
 
+namespace unwindstack {
+
 void ResetLogs() {
   g_fake_log_buf = "";
   g_fake_log_print = "";
@@ -46,6 +47,8 @@
   return g_fake_log_print;
 }
 
+}  // namespace unwindstack
+
 extern "C" int __android_log_buf_write(int bufId, int prio, const char* tag, const char* msg) {
   g_fake_log_buf += std::to_string(bufId) + ' ' + std::to_string(prio) + ' ';
   g_fake_log_buf += tag;