vector: fix functions description

vector: rm unnecessary cast

Merge back changes from stable-1.5

Change conversion operator from T() to T&() in v<>

persistent_ptr: add unsigned index operator 1.5

Ref: #103

Vector skeleton

Merge back changes from stable-1.5

Fix v swap, assignment operators and constructors.

Fix include in one more header

Fix headers inclusion for system headers 

Merge back changes from stable-1.5

Fix headers inclusion for system headers

Add info about pmemcheck annotations in readme

Fix ambiguous comments in make_persistent array

Changes are applied to files that were created after stable-1.5

Assignment operators didn't work correctly because operatorT()
was not really a const function and this_type (used in those functions)
was not decalared. This resulted in compile error while trying to
assign v<> of different types.

Additionally v<> constructor taking const T& as parameter is not
needed. Using it would mean assigning some value to underlaing val
in v<>, but first call to get() would run constructor (which would
potentially change the value).

Implement property that allows to subtract an iterator from another

Imported from llvm-mirror/libcxx@5ae92f0

Change breaking literals rule in clang.format

test: fix includes and flags

Add Valgrind annotation support