[unique.ptr.single] Align preconditions and postconditions with the guidelines

According to https://github.com/cplusplus/draft/wiki/Specification-Style-Guidelines#formatting-declarations-and-definitions, conditions should be expressed as `<expr> is true` instead of simply `<expr>`. It seems that `std::unique_ptr` specification does not comply with that.

This PR updates all such places that I have spotted.

Author: MikailBag

source/memory.tex

@@ -2446,7 +2446,7 @@
 \pnum
 \ensures
 \tcode{get()} yields the value \tcode{u.get()}
-yielded before the construction. \tcode{u.get() == nullptr}.
+yielded before the construction. \tcode{u.get() == nullptr} is \tcode{true}.
 \tcode{get_deleter()} returns a reference
 to the stored deleter that was constructed from
 \tcode{u.get_deleter()}. If \tcode{D} is a reference type then
@@ -2492,7 +2492,7 @@
 \pnum
 \ensures
 \tcode{get()} yields the value \tcode{u.get()}
-yielded before the construction. \tcode{u.get() == nullptr}.
+yielded before the construction. \tcode{u.get() == nullptr} is \tcode{true}.
 \tcode{get_deleter()} returns a reference
 to the stored deleter that was constructed from
 \tcode{u.get_deleter()}.
@@ -2549,8 +2549,8 @@
 
 \pnum
 \ensures
-If \tcode{this != addressof(u)},
-\tcode{u.get() == nullptr},
+If \tcode{this != addressof(u)} is \tcode{true},
+\tcode{u.get() == nullptr} is \tcode{true},
 otherwise \tcode{u.get()} is unchanged.
 
 \pnum
@@ -2588,7 +2588,7 @@
 
 \pnum
 \ensures
-\tcode{u.get() == nullptr}.
+\tcode{u.get() == nullptr} is \tcode{true}.
 
 \pnum
 \returns
@@ -2607,7 +2607,7 @@
 
 \pnum
 \ensures
-\tcode{get() == nullptr}.
+\tcode{get() == nullptr} is \tcode{true}.
 
 \pnum
 \returns
@@ -2644,7 +2644,7 @@
 \begin{itemdescr}
 \pnum
 \expects
-\tcode{get() != nullptr}.
+\tcode{get() != nullptr} is \tcode{true}.
 
 \pnum
 \returns
@@ -2700,7 +2700,7 @@
 \begin{itemdescr}
 \pnum
 \ensures
-\tcode{get() == nullptr}.
+\tcode{get() == nullptr} is \tcode{true}.
 
 \pnum
 \returns
@@ -2726,7 +2726,7 @@
 
 \pnum
 \ensures
-\tcode{get() == p}.
+\tcode{get() == p} is \tcode{true}.
 \begin{note}
 The postcondition does not hold if the call to \tcode{get_deleter()}
 destroys \tcode{*this} since \tcode{this->get()} is no longer a valid expression.