add dataTableOutput() and renderDataTable() for the DataTables library

not yet done, but at least paging is working now
the ... argument is not really used
document renderDataTable() and dataTableOutput()
a simple implementation of global searching
make sure the data has two dimensions
disable default sorting
implement sorting; the very basic features are there now, but this still needs a lot of improvement in terms of details
now we can sort multiple columns: press Shift and click the column headers
index from 0, sigh
implement searching by columns
write a datatable output binding; the column names and action url are passed from renderDataTable() to the output binding
use the nicer bootstrap style
remove the ColumnFilter plugin; it is too heavy, and I just added the <input> by myself and implemented searching by individual columns
the searching should use intersection instead of union
css for the processing indicator
BSD license for DataTables
allow users to pass initialization options to datatables
roxygenize
debouncing is done single-handedly, thanks to Joe's smart debounce() function
roxygenize