add new constants to ruby binding

add new hook type UC_HOOK_MEM_READ_AFTER, adapted from PR #399 by @farmdve. updated all bindings, except Ruby & Haskell

- in appveyor, install clang and cmake in cygwin, enable package upgrades, and build cmocka and enable testing for gcc only
- in `gitignore`, ignore generated cmocka folder
- in travis, use brew in osx to install cmocka, and enable testing for gcc and clang on os x and linux
- in `Makefile`, change to use `uname -s` to determine os type
- make `install-cmocka-linux.sh`, a simple shell script to download and install cmocka on linux
- in `bindings/Makefile`, enable `make -c` to call subdirectory makefiles instead of `cd [dir] && make` and include environment variables for runtime access to generated libraries
- in `samples/Makefile`, change to use `uname -s` to determine os type, remove `clean_bins` from `all` command, and include `Werror` for compile strictness
- in `tests/unit/Makefile`, add `cflags` for compile time access to cmocka headers and library, include execute vars for runtime access to cmocka and unicorn libs
- in `tests/unit/test_tb_x86.c`, comment out assert that would not compile 

Remove unmapped/freed memory regions from the object property list.

This commit fixes the following issues:
- Any unmapped/free'd memory regions (MemoryRegion instances) are not
  removed from the object property linked list of its owner (which is
  always qdev_get_machine(uc)). This issue makes adding new memory
  mapping by calling mem_map() or mem_map_ptr() slower as more and more
  memory pages are mapped and unmapped - yes, even if those memory pages
  are unmapped, they still impact the speed of future memory page
  mappings due to this issue.
- FlatView is not reconstructed after a memory region is freed during
  unmapping, which leads to a use-after-free the next time a new memory
  region is mapped in address_space_update_topology().

Tweak some names in a few places, encapsulate the uc_context struct to hide it from users for some reason

Change save/restore API to have explicit alloc/free functions. Python has explicit save/update functions.

Merge branch 'feat/reg_save_restore' of https://github.com/rhelmot/unicorn into rhelmot-feat/reg_save_restore

Update test_hang.c

Fixed ARM THUMB Haskell sample as per Issue #638