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)
[class] Fix unclear phrase "only one" to clearer phrase "at most one"
used in [class.union], to make it more obvious that a union can have
no active members.
[stack.defn] Fix swap signature.

Reported by Stephan T Lavavej. Fixes #242
[util.smartptr.shared.const], [util.smartptr.weak.const] Remove "the"

Fixes #335
[futures.overview] Add ArgTypes... to swap declaration.

Fixes #336
[func.bind.bind] Fix "template parameter back" typo.

Fixes #316
[memory.syn] Change "template functions" to "function templates"

Fixes #302
Merge pull request #354 from jwakely/issue-242

[stack.defn] Fix swap signature.
[utility] Add index_sequence et al to the library index.

Addresses #245
[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.