Tidy NBLAST and plotting tests and functions
Add to tests for fc_subscoremat
Add ability to return normalised forward scores from fc_subscoremat + test
Add documentation for fc_subscoremat
Merge pull request #2 from ajdm/fc_subscoremat

fc_subscoremat changes + tests
simplify handling of scoremat parameter
Avoid subsetting big matrix by names

* fetching names is expensive so cache and then use numeric
  indices
* I noticed ~ 20x speedup on tests datasets
Add ff as a suggested package
check that we can give an ff matrix as input to fc_subscoremat
two more tests

* which pass
factor out a function to extract diagonal terms from fc_subscoremat

* getting diagonal terms out of an ff matrix is actually fast like this
* this is also the fastest way to acc ess a big.matrix
DOC: also mention ff matrices
Add ability to download and attach ff objects + test
Add ability for fc_attach_bigmat to handle ff objects
fix import error in diagonal()
check that original fc_nblast and fc_subscoremat agree
correct handling of queries when the result has a singleton dimension

* this has been a general problem of fc_subscoremat
fix bug in extracting diagonal of bigmatrix objects
reimplent fc_nblast using fc_subscoremat
reimplement fc_sub_distmat using fc_subscoremat

* note that results will not be identical because fc_sub_distmat returns 
  matrices with row/column ordering according to the underlying distance
  matrix
* whereas fc_subscoremat respects the requested ordering
* this will result in different dendrograms since in many cases dendrogram
  ordering is driven by input order not anything calculated from the data