Added the ability to accumulate coef stats across encodings

This commit added the ability to accumulate the coef stats across
different encodings using an intermediate binary stats files. The
accumulation happens only the binary stats file exists in current
directory. The encoder needs to be built with "ENTROPY_STATS" to
allow the output. The commit also fixed a few formating issues in
output stats file.

Change-Id: Ib1a41180aa554845cf51e4421a230b128a3a82b4