buffer: bugfix (v2) consolidate the offset and readptr

- It didn't make sense to make the user keep count of the different
  types of read pointers, instead do the relative calculation at the
  lowest level (wraparoundRead)
- Added further tests to prove out that readPtr is being updated
  properly in wraparoundRead)
- Fixed wraparoundRead, as it was relying on the dataInterface->read to
  read until the "end". The "end" was fixed in the bugfix #1 to be the
  end of the queue instead of the mmaped buffer.
- took out addtionalBoundaryCheck from wraparoundRead, as it was no
  longer needed

Tested: Unit tested

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: I101360223597d197362dc1dbe4a27601da09933f
diff --git a/include/data_interface.hpp b/include/data_interface.hpp
index bf91817..8292143 100644
--- a/include/data_interface.hpp
+++ b/include/data_interface.hpp
@@ -18,7 +18,7 @@
     /**
      * Read bytes from shared buffer (blocking call).
      *
-     * @param[in] offset - offset to read from
+     * @param[in] offset - offset to read from relative to MMIO space
      * @param[in] length - number of bytes to read
      * @return the bytes read
      */
@@ -28,7 +28,7 @@
     /**
      * Write bytes to shared buffer.
      *
-     * @param[in] offset - offset to write to
+     * @param[in] offset - offset to write to relative to MMIO space
      * @param[in] bytes - byte vector of data.
      * @return return the byte length written
      */