instantiation -> specialization in [refwrap]

To match the wording of http://cplusplus.github.io/LWG/lwg-active.html#2106 (The wording of 2106 is taken from here, but we decided to use the term "specialization".
Fix typography of "C." (spacing)
[adjacent.difference] Use code font for *i expression.

Fixes #287
[new.delete.single], [smartptr.util.getdeleter] Replace literal 0 with nullptr.

Fixes #243 and #244
[over.ics.rank] Correct the example in p3.1.5 to demonstrate that
bullet; previously the example was ordered by 3.1.1 because one of
the overloads did not require a qualification conversion.
[refwrap] Use injected class name in reference_wrapper special member functions
[util.smartptr.shared.const]
[util.smartptr.shared.obs]
Replace literal 0 with nullptr.
[atomics.syn] Fix typo by replacing ')' with '_'

Fixes #359
Merge pull request #360 from redboltz/replace_0_with_nullptr_on_shared_ptr

[util.smartptr.shared.const]
[util.smartptr.shared.obs]
Replace literal 0 with nullptr.
Merge pull request #358 from K-ballo/refwrap-injected-class-name

[refwrap] Use injected class name in reference_wrapper special member fu...
Fix several omissions of semicolon.
Merge pull request #361 from kariya-mitsuru/add_semicolon

Fix several omissions of semicolon.
[basic.types] Italicize the definitions of 'incompletely-defined object
type' and 'incomplete type', and add index entries.
[expr.prim.general] Use code font for ~.
[cpp] Fix font of # in non-directive.
[gram] Don't convert one space to two after a `.` or `!` in the grammar.
These do not mark the end of a sentence.
Use a consistent size and position for all tildes.
Replace all '\sim's with '\~'s, to give more consistent formatting for ~s.
Merge pull request #348 from tkoeppe/typography1

Fix typography of "C." (spacing)
[basic.lookup.classref] Use code font for `~`.