work on sign in tensor product
Merge branch 'master' of https://github.com/MarkWatkins2014/lmfdb into mine

* 'master' of https://github.com/MarkWatkins2014/lmfdb:
  add comment
  fix typo
  Do the semistable x semistable correctio
small change to mark's corrections at nasty primes
go for dinner
adjusting base_ring for euler factors
change renormalisation
some documentation at the end
change link to github, not googlecode