[lex.literals] Improve presentation of tables.

Break lines better, and add horizontal rules (to make "rowspaning
cells") to clarify the scope of table entries.

Author: tkoeppe

source/lex.tex

@@ -1367,7 +1367,7 @@
 \end{note}
 
 \begin{floattable}{Character literals}{lex.ccon.literal}
-{lllll}
+{l|l|l|l|l}
 \topline
 Encoding & Kind & Type & Associated char- & Example \\
 prefix & & & acter encoding & \\
@@ -1376,12 +1376,12 @@
 \defnx{ordinary character literal}{literal!character!ordinary} &
 \keyword{char} &
 ordinary &
-\tcode{'v'} \\
+\tcode{'v'} \\ \cline{2-3}\cline{5-5}
  &
 non-encodable ordinary character literal &
 \keyword{int} &
 literal &
-\tcode{'\textbackslash U0001F525'} \\
+\tcode{'\textbackslash U0001F525'} \\ \cline{2-3}\cline{5-5}
  &
 ordinary multicharacter literal &
 \keyword{int} &
@@ -1391,12 +1391,12 @@
 \defnx{wide character literal}{literal!character!wide} &
 \keyword{wchar_t} &
 wide &
-\tcode{L'w'} \\
+\tcode{L'w'} \\ \cline{2-3}\cline{5-5}
  &
 non-encodable wide character literal &
 \keyword{wchar_t} &
 literal &
-\tcode{L'\textbackslash U0001F32A'} \\
+\tcode{L'\textbackslash U0001F32A'} \\ \cline{2-3}\cline{5-5}
  &
 wide multicharacter literal &
 \keyword{wchar_t} &
@@ -1706,7 +1706,8 @@
 {llp{2.6cm}p{2.3cm}p{4.7cm}}
 \topline
 Encoding & Kind & Type & Associated & Examples \\
-prefix & & & character encoding & \\
+prefix   &      &      & character  & \\
+         &      &      & encoding   & \\
 \capsep
 none &
 \defnx{ordinary string literal}{literal!string!ordinary} &
@@ -1717,7 +1718,7 @@
 \tcode{L} &
 \defnx{wide string literal}{literal!string!wide} &
 array of $n$\newline \tcode{\keyword{const} \keyword{wchar_t}} &
-wide literal encoding &
+wide literal\newline encoding &
 \tcode{L"wide string"}\newline
 \tcode{LR"w(wide raw string)w"} \\
 \tcode{u8} &