Rename pgfault and pgmajfault fields

  optional string process_name = 2;

  // # of page-faults

  optional int64 pgfault = 3;

  optional int64 page_fault = 3;

  // # of major page-faults

  optional int64 pgmajfault = 4;

  optional int64 page_major_fault = 4;

  // RSS

  optional int64 rss_in_bytes = 5;