Closes #744. X[Y, c(.), by=.EACHI] doesn't segfault
Merge branch 'fix-744'
Closes #474. Added .onUnload method

This ensures datatable.so is properly unloaded on 'detach'.
Merge branch 'fix-474'
Added link to NEWS
Merge branch 'fix-474'
Closes #500. lapply(L, "[", Time ==3L) works as expected.

Subset data.tables using lapply doesn't redirect to `[.data.frame` anymore.
Merge branch 'fix-500'
Fixed link.
Closes #754. Updated BugReports link in DESCRIPTION.
DT[, c(.SD, …), by=.] optimised, #735 task list 1,2.
setDT over-allocates DT if not 'selfrefok'.
raised 'if' on j-optim check in is.name(jsub)

When 'j' is a symbol, optimisation should happen only if it's .SD.
More .SD optimisations #735 task list 3, 4 and 5

.SD[1], .SD[1L], head(.SD, 1) in `j` alone or along with c(..) are now optimised for speed internally.
Implemented setdiff #547 task list 1. Not exported.

First attempt at setdiff for DTs
Merge branch 'Feature-735'

Conflicts:
	inst/tests/tests.Rraw
Merge branch 'Feature-547'
Added setdiff_ to devtesting.

Tests should run smoothly.
Merge branch 'Feature-547'
Closes #604. by=.EACHI is implemented for not joins.

X[ !Y, j, by=.EACHI] now works as intended.