Clarify newFileSize & mappedSize params in memfiles.open() docs
Update posix open() call to incl. permissions

This explicitly grants user read/write access to newly-created mmap files. Previously, on some systems files would be created but could not be re-opened as the user lacked sufficient permissions.
Fix missing import in nimprof.nim when --threads:on
Revert 876cad3a - making nimprof fix on a new branch
Merge pull request #1182 from boydgreenfield/devel

Clarify newFileSize & mappedSize params in memfiles.open() docs