Explain pepc_npm parameter and rearrange a bit.
Merge pull request #11 from bsteinb/master

Explain pepc_npm parameter and rearrange a bit.
PNFFT: use ptrdiff_t for loop variables in fortran test
Merge branch 'master' of https://github.com/scafacos/scafacos
manual: rewrite 'compiling and building' in latex