tidying
join protocol and tests
join for persistent vectors
fix join with reduced dimensionality
remove square constraint for main-diagonal
broadcasted addition and subtraction
fix for sequence element-map
more sequence fixes
broadcasting for persistent vector add/sub
more broadcasting fixes
tidy
fix sub, implement default negation protocol
negate test
fix coercions for persistent vectors
improve construction of persistent vector matrices
fix mapmatrix for non-vectors
misc edits
test rotate function
add rows and columns functions to API
fix doc