Fixed a bug in _array_to_string
Changed the way to compute state diff

Improvement on handling warmup options
Added sparse_dot functions
Since L0 is not actually used, replace it with max_stepsize at all
places
Removed the redundant tbl_inter_result from both optimizers
Use reference to pass all arguments in C++

Also set default max_iter to be 10000
A tiny change
Implementing active set method for FISTA

Set up the control structure
Finished active-set method for FISTA, but it is extremly slow

There might be a bug, or maybe it just does not work.

Need more exploration
Fixed the bug in FISTA active set method

It is faster on Postgres, but on GPDB it is really slow and the result
is wrong. There is still a bug.
Bug in GPDB for active-set method is fixed

In GPDB, numRows must be explicitly reset to 0 at the end of final
function.

Added this into both optimizers.