Inplace reduction functions

Inplace reduction functions (including sum!, prod!, maximum!, minimum!, all!, and any!) have been within the Base for a while. This PR exports them with a modified interface that is safe & flexible.
add documentation for sum! and friends
add an entry to NEWS.md about the reduction functions that allow pre-allocated output
add the link to 6197 in news
replace unbox warning with an assertion

this code is fine and the warning is not needed.
Merge pull request #6197 from lindahua/dh/inplacesum

Reduction functions with pre-allocated output storage.
remove jl_get_exception_str. fixes #6199

a better name for this function would be jl_cause_segfault().
Merge branch 'master' of github.com:JuliaLang/julia
Update package generation for changes in #6191
fix typos
Merge pull request #6206 from catawbasam/patch-3

fix typos
Typo
fix 'parse("immutable X end")' show bug
add mean!, which allows pre-allocated output
add documentation for mean!
Merge pull request #6207 from lindahua/dh/mean3

add mean!, which allows pre-allocated output
improve printing of address op exprs (e.g., :(&x))
make sjlj compatible with msvc compiler
work around msvc bug where .model must be on its own line or it forgets about it
forgot the same update as previous for setjmp