api: expose rate control params via x265_param_parse() and CLI

Adds range checks for qCompress, which has documented limits. The others have
very minimal explanations; so I'm not adding them to the CLI help. Users should
not touch them unless they know what they are doing.

Note this commit doesn't bump X265_BUILD since no new params were added.
cli: cleanup CLI help, add 'verbose' tier

Remove a lot of uncommon features from the initial help output, require
--log-level debug --help to see it all
api: cleanup comments
docs: document RC params, at least minimally
search: ugly bias hack for bidir with psy-rd
param: add --tune grain
doc: fix sub-title depth

Single dash was already used by a higher section
cudata: remove default argument
search: made separate functions for encoding cbfs in xEstimateResidualQT()
search: made a function for null cost calculation in xEstimateResidualQT()
[REVIEW PATCH/OUTPUT CHANGED]search: removed multiple encode Coefficients from estimateResidualQT()

Tried to remove multiple encode coefficients from estimateResidualQT() function.
Coefficients are encoded in three stages: Once for calculation of distortion and twice for split and unsplit
block cost calculation. I have given comments where I have changed the code.
fix typo