tools: put all host-side code into host_tool namespace

To avoid confusion and organize the code itself more cleanly, place the
host-side code into its own namespace.

Change-Id: I573eb0494eb59874adb1d1eadc502499e928e396
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/tools/crc.hpp b/tools/crc.hpp
index f377a20..c335ed2 100644
--- a/tools/crc.hpp
+++ b/tools/crc.hpp
@@ -3,6 +3,9 @@
 #include <cstdint>
 #include <vector>
 
+namespace host_tool
+{
+
 /**
  * Generate the CRC for a payload (really any bytes).
  *
@@ -13,3 +16,5 @@
  * @return the CRC value
  */
 std::uint16_t generateCrc(const std::vector<std::uint8_t>& data);
+
+} // namespace host_tool