Automated timer interval configuration

[jovanbulck]

A fully automated single-stepping timer configuration benchmark program would repeatedly interrupt an enclaved nop instruction slide, each time adjusting the current timer interval guess -- in a binary search fashion based on the previous in-enclave instruction pointer (zero-step vs. multi-step).

[jovanbulck]

this should be relatively straightforward now using app/baresgx (although the timer interval seems to change slightly depending on the application); probably #87 should be implemented first