level: in CRF/CQP encodes, allow user specifed level to increase stream level

See the comment
common: introduce x265_slurp_file, reads data from file to string buffer.

--HG--
extra : amend_source : e897c0743ce844aa7c8629dc896b4fecb930cdf8
param: add more param options to print as string

--HG--
extra : amend_source : 009bb75a85ace4d0be5c7902a7b856bcc63d5c6e
param: use dashes consistently in param2string
rc: store final cu counts in frameStats as a percentage of total # cus

there exists a mismatch in the total no. of 16x16 blocks calculated between encoder and RC.
rate control counts no. of 16x16 blocks without considering the border extension of source pic.
keeping cu stats as percentage avoid this problem when used later in RC's 2nd pass.

--HG--
extra : amend_source : ffb2395d0d2732a0586dec889ff5502a3961566f
param: keep the total frame count of the input video in param.

to be used in 2 pass. In case this is not available, the value can remain as 0.

--HG--
extra : amend_source : c8500c03fb8124e8c220f33ea8b6c02a205aed19
rc: init RC data for second pass in a multi pass encode
frameencoder: store reflagrows as a member variable
cmake: nit - about target arch strings
rc: nits
param: fix typo in d1d5b377294e