Change a few stray headings to sentence case

Fixes #1200 and #1201.

Author: tkoeppe

source/compatibility.tex

@@ -1279,7 +1279,7 @@
 binary representation of the required template specializations of
 \tcode{std::complex} may not be compatible with this International Standard.
 
-\rSec2[diff.cpp03.input.output]{Clause \ref{input.output}: Input/output library}
+\rSec2[diff.cpp03.input.output]{Clause \ref{input.output}: input/output library}
 
 \ref{istream::sentry},
 \ref{ostream::sentry},
@@ -1667,7 +1667,7 @@
 Valid \CppXIV code that uses such a top-level namespace,
 e.g., \tcode{std2}, may be invalid in this International Standard.
 
-\rSec2[diff.cpp14.utilities]{Clause \ref{utilities}: General utilities library}
+\rSec2[diff.cpp14.utilities]{Clause \ref{utilities}: general utilities library}
 
 \ref{func.wrap}
 \change Constructors taking allocators removed.

source/future.tex

@@ -2001,7 +2001,7 @@
 Nothing.
 \end{itemdescr}
 
-\rSec1[depr.meta.types]{Deprecated Type Traits}
+\rSec1[depr.meta.types]{Deprecated type traits}
 
 \pnum
 The header
@@ -2028,7 +2028,7 @@
 \tcode{T} is a literal type~(\ref{basic.types}), and a base-characteristic of
 \tcode{false_type} otherwise.
 
-\rSec1[depr.iterator.primitives]{Deprecated Iterator primitives}
+\rSec1[depr.iterator.primitives]{Deprecated iterator primitives}
 
 \rSec2[depr.iterator.basic]{Basic iterator}
 

source/iostreams.tex

@@ -14735,7 +14735,7 @@
 \end{example}
 \end{itemdescr}
 
-\rSec3[fs.op.weakly_canonical]{Weakly Canonical}
+\rSec3[fs.op.weakly_canonical]{Weakly canonical}
 
 \indexlibrary{\idxcode{weakly_canonical}}%
 \begin{itemdecl}

source/threads.tex

@@ -139,7 +139,7 @@
 the implementation as specified in~\ref{time.clock} do not throw exceptions.
 \end{note}
 
-\rSec2[thread.req.lockable]{Requirements for Lockable types}
+\rSec2[thread.req.lockable]{Requirements for \tcode{Lockable} types}
 
 \rSec3[thread.req.lockable.general]{In general}