Support multiple slicing criteria given by file

The slice output file is opened in the append mode so that all the
slices of the multiple criteria is written to the output slice file.
Perhaps we should refine the output format in the future.
Add test containing multiple slicing criteria
Refine the README.md file according to the wiki
Don't compare the tid for all trace file visit

We should re-consider carefully the cases one by one carefully when
comparing the thread id matching load/store and basic blocks. This
should be done after we guarantee the load/store sequence when writing
to the trace file.
Cast the pages * LOAD_FACTOR to be a long first

Make sure the entryCacheBytes be divided by the page_size. Previously,
there is a bug there since the total entryCacheBytes may not be divided
by the page_size.
Rename the pthread id var to tid from pid

And make some trivial refinements to the comments.