Add a function to free g_exp_table.

Even though g_exp_table has to be global (used in #define), it's better to avoid requiring other module to directly access it.
init_context directly has a QP parameter, instead of passing an encoder_control*

This makes context less tightly coupled with encoder.
Remove cabac global variable
Moved context information inside cabac_data.

This is required in order to be able to work on parallelism.
Clean up tabs and whitespaces
Merge commit 'e15a86268def51984b2ff4efc966ddfa74ca3fa2'