Fix mmap with offset on Windows

query allocation granularity (64k on Windows, larger than page size which is 4k),
ensure offset to MapViewOfFile is a multiple of the granularity

add a test for mmap with offset
fix szfile and szarray values

replace 0xffffffff with typemax(Uint32)
add a test with a larger offset than 64k
use div(a, b) instead of ifloor(a/b)
add extra error message info from Windows API
WINDOWS: quiet the wine cross-build
/bin/sh shebang instead of /bin/bash in deps/jlchecksum
Merge pull request #7242 from tkelman/mmap_windows

Fix mmap_array with offset on Windows
Add `make install` instructions.

Adds a description of using the `prefix` variable along with `make install` in addition to the symlink or `PATH` options. Also, changing it to a bullet-list makes it clearer that they are alternatives, not ordered steps to follow.
Update CONTRIBUTING.md

Close #7273
Eliminate bash-isms
Merge pull request #7270 from lucasb-eyer/patch-1

Add `make install` instructions.
Merge pull request #7268 from JuliaLang/sf/dontbashme

/bin/sh shebang instead of /bin/bash in deps/jlchecksum
revised poll_fd tests
standardized event property testing
implement #6563 to merge close #4401