mmap-alloc: Improve tests for permissions, fix realloc bugs

- Add the ability to parse /proc/<pid>/maps on Linux, and
  incorporate this into existing tests in order to verify
  permissions
- Remove checks for allocation at the 0 page, as it turns
  out that these are unnecessary on all platforms that we
  support (Linux, Mac, Windows)
- Change the way boolean configuration functions work for
  MapAllocBuilder (instead of xxx() and no_xxx(), we now
  supply a single xxx(xxx: bool) method that accepts a
  boolean indicating whether the configuration should be
  on or off)
- Move tests module into separate file

Closes #80, #83
Closes #72 by making it unnecessary since this commit removes
the use case for mark_unused

mmap-alloc/CHANGELOG.md

@@ -18,11 +18,22 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added `commit` and `uncommit` methods on Windows
 - Added the ability to configure whether `alloc` commits memory
 - Added documentation about instruction cache incoherency
-- Added support for full Alloc API (`shrink_in_place`, `grow_in_place`, `realloc`)
- - In Linux, these functions can use `mremap` to grow/shrink beyond the size of a the pagesize
+- Added support for full Alloc API (`shrink_in_place`, `grow_in_place`,
+ `realloc`)
+ - In Linux, these functions can use `mremap` to grow/shrink beyond the size
+ of a the pagesize
+- Added tests for memory permissions on Linux by parsing `/proc/<pid>/maps`
 
 ### Removed
 - Removed `commit` method on on Linux and Mac
+- Removed tests for `mmap`s at NULL on Linux and Mac, as it turns out they are
+ guaranteed not to happen
+
+### Changed
+- Changed the way boolean configuration methods on `MapAllocBuilder` work
+ (previously, for each configuration option, there was a pair of methods to
+ enable and disable that option; now, there's a single method that accepts a
+ boolean indicating whether the option should be enabled)
 
 ### Fixed
 - Fixed a bug that prevented compilation on 32-bit Windows