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/Memory.cpp b/libunwindstack/Memory.cpp
index 9e46509..8c36055 100644
--- a/libunwindstack/Memory.cpp
+++ b/libunwindstack/Memory.cpp
@@ -28,7 +28,11 @@
 
 #include <android-base/unique_fd.h>
 
-#include "Memory.h"
+#include <unwindstack/Memory.h>
+
+#include "Check.h"
+
+namespace unwindstack {
 
 bool Memory::ReadString(uint64_t addr, std::string* string, uint64_t max_read) {
   string->clear();
@@ -245,6 +249,11 @@
   return true;
 }
 
+MemoryRange::MemoryRange(Memory* memory, uint64_t begin, uint64_t end)
+    : memory_(memory), begin_(begin), length_(end - begin) {
+  CHECK(end > begin);
+}
+
 bool MemoryRange::Read(uint64_t addr, void* dst, size_t size) {
   uint64_t max_read;
   if (__builtin_add_overflow(addr, size, &max_read) || max_read > length_) {
@@ -253,3 +262,5 @@
   // The check above guarantees that addr + begin_ will not overflow.
   return memory_->Read(addr + begin_, dst, size);
 }
+
+}  // namespace unwindstack