[WIP] Experimental Sketch API for Atomic MultiLog

[ujvl]

Initial sketch-related API additions to atomic_multilog:

  void add_sketch(sketch_name : str, field_name : str, filter_name : Optional[str]);
  void remove_sketch(sketch_name : str);
  size_t estimate_frequency(sketch_name : str, value : str);
  map<val : freq> get_heavy_hitters(sketch_name : str);
  double evaluate_metric(sketch_name : str, metric: enum);

How was this patch tested?

WIP

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/confluo-prb/351/
Test PASSed.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/confluo-prb/352/
Test PASSed.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/confluo-prb/354/
Test PASSed.