create experimental branch, updated welcome message
A complete change of Pd data structure: 

Pd[f, i] is no longer fundamental. Rather, it is transformed into PdT[f,
PdVars[i]].
Updated a few ibp rules. Changed string Sampi to symbol Sampi
IBP written. Now TrySimp and Ibp can take general levels to try rules.
Updated typeset of time derivative
Added a double dot and H double dot. Updated IBP counting
(nonsignificant)
Support for parallelization. Currently only useful for very complicated
tensors which every term needs some time to process.
Initial support for LaTeX and MathML output.
Exporting to TeX improved.
Issue fixed about TeX output (like (partial_0 phi)^2)
TeX output improved
Don't start FrontEnd definitions if not started in GUI
Remove additional new line if an equation starts with "-"
Use SyntaxForm to determine when TagBox should add parenthesis.
Fixed parallel performance by not doing simpF in parallel.

Note that simpF is not the slow part. Also it helps cancellation between
terms. If simpF is done in parallel, cancellation between terms on
different kernels is no longer possible.

One can do two passes and first do simpF on parallel. But there should
be no point to do it considering it is fast.
Simp family functions are rewritten with cleaner method and definitions.
Replace TensorContract to mark contracted pairs. This is cleaner than
map functions onto TensorContract.
removed SyntaxForm for Standard form -- this may produce problems in
complicated tensors like those in dBianchi2
Now PdHold and IdHold works with Simp[.., "Method"->"Fast"]
Added Pm2 to invert Laplacian.