Modify code to show results per iteration for algorithm analysis.
Test the implementation is correct or not.

Tried many frame numbers. For each number, we compute the energy
and compare it with the implementation in master branch. Now we
confirm our implementation is correct.
Add a base Solver class.

When we start to implement a new algorithm, we can implement a
derived class and implement all the virtual functions. ArapSolver
is a good example to start.
Many updates:
Build the framework for AdmmSolver.
Change some variable names in ArapSolver.
Unfinished:
Build matrix and rhs for linear solve in AdmmSolver.
Finish implementing ADMM solver.
Test required! Also start to add ADMM solver in main.cc.
Replace RegisterData with constructor.
The framework for testing algorithm in main.cc is done. Change the
Merge correct version of admmsolver.cc.
Switch to AdmmSolver in main.cc.
Delete unnecessary eigenvalue code in admmsolver.cc.
Delete unnecessary simple matrix test code in admmsolver.cc.
Add make clean in build.sh.
Fix array overflow in admmsolver.cc.
Try with SparseLU solver in solver.h.
Build option, solver position and sanity check for solver.
Change build option from Release to Debug.
Move solver_ from Solver to Derived solver classes in case
different solvers are needed (e.g., the matrix is not PSD).
Sanity check the norm of the residual from solver.
Fix bugs in computing energy.
add input for rho too.
Merge verifed AdmmSolver from debug.
The AdmmSolver has been fully tested in debug branch.
Minor changes to some output strings.
Add options to turn on/off the debug info. Turning on these functions
will slow down the optimization severely, however it is still highly
recommended to turn on them when we first run a demo, and if it passes
all the tests, then we can safely turn them off in the future.
Add Energy class.
Untested.
Apply Energy in the whole project.
Energy has been tested on AdmmSolver: first use stdout to output
all kinds of energies, then use Energy. The results are the same.
Move all parameters into main's input args.
Tested with ArapSolver and AdmmSolver.
Rename AdmmSolver to AdmmFreeSolver.