Fix typos (#6765)

* Update setDT.Rd

removed redundant full-stop.

* Update cdt.Rd

tweaks to cdt

* Update dcast.data.table.Rd

remove redundant space

man/cdt.Rd

@@ -2,14 +2,14 @@
 \alias{cdatatable}
 \title{ data.table exported C routines }
 \description{
-  Some of internally used C routines are now exported. This interface should be considered experimental. List of exported C routines and their signatures are provided below in the usage section.
+  Some of the internally used C routines are now exported. This interface should be considered experimental. List of exported C routines and their signatures are provided below in the usage section.
 }
 \usage{
 # SEXP DT_subsetDT(SEXP x, SEXP rows, SEXP cols);
 # p_DT_subsetDT = R_GetCCallable("data.table", "DT_subsetDT");
 }
 \details{
-  Details how to use those can be found in \emph{Writing R Extensions} manual \emph{Linking to native routines in other packages} section.
+  Details on how to use these can be found in the \emph{Writing R Extensions} manual \emph{Linking to native routines in other packages} section.
   An example use with \code{Rcpp}:
 \preformatted{
   dt = data.table::as.data.table(iris)

man/dcast.data.table.Rd

@@ -3,7 +3,7 @@
 \alias{dcast}
 \title{Fast dcast for data.table}
 \description{
-  \code{dcast.data.table} is \code{data.table}'s long-to-wide reshaping tool. In the spirit of \code{data.table}, it is very fast and memory efficient, making it well-suited to handling large data sets in RAM.  More importantly, it is capable of handling very large data quite efficiently in terms of memory usage. \code{dcast.data.table} can also cast multiple \code{value.var} columns and accepts multiple functions to \code{fun.aggregate}. See Examples for more.
+  \code{dcast.data.table} is \code{data.table}'s long-to-wide reshaping tool. In the spirit of \code{data.table}, it is very fast and memory efficient, making it well-suited to handling large data sets in RAM. More importantly, it is capable of handling very large data quite efficiently in terms of memory usage. \code{dcast.data.table} can also cast multiple \code{value.var} columns and accepts multiple functions to \code{fun.aggregate}. See Examples for more.
 }
 
 \usage{

man/setDT.Rd

@@ -2,7 +2,7 @@
 \alias{setDT}
 \title{Coerce lists and data.frames to data.table by reference}
 \description{
-  In \code{data.table} parlance, all \code{set*} functions change their input \emph{by reference}. That is, no copy is made at all, other than temporary working memory, which is as large as one column.. The only other \code{data.table} operator that modifies input by reference is \code{\link{:=}}. Check out the \code{See Also} section below for other \code{set*} function \code{data.table} provides.
+  In \code{data.table} parlance, all \code{set*} functions change their input \emph{by reference}. That is, no copy is made at all, other than temporary working memory, which is as large as one column. The only other \code{data.table} operator that modifies input by reference is \code{\link{:=}}. Check out the \code{See Also} section below for other \code{set*} function \code{data.table} provides.
 
   \code{setDT} converts lists (both named and unnamed) and data.frames to data.tables \emph{by reference}. This feature was requested on \href{https://stackoverflow.com/questions/20345022/convert-a-data-frame-to-a-data-table-without-copy}{Stackoverflow}.