[llvm-exegesis] Add an analysis mode.

Summary:
The analysis mode gives the user a clustered view of the measurement results.
Next steps are (requires the split ok AsmTemplate.Name into {mnemonic, mode}):
 - Show the sched class.
 - Highlight any inconsistencies with the checked-in data.

Reviewers: gchatelet

Subscribers: mgorny, llvm-commits, tschuett

Differential Revision: https://reviews.llvm.org/D46865

llvm-svn: 332344