Merge pull request #783 from hintjens/master

Problem: misuse of include files in zsys
Update CONTRIBUTING.md
Problem: PKG_CHECK_MODULES doesn't add to LIBS on android
Solution: Add -lzmq to LIBS manually
Merge pull request #785 from jemc/master

Problem: PKG_CHECK_MODULES doesn't add to LIBS on android
Added base16 support to zarmour
Merge pull request #786 from lovmoen/master

Problem: zarmour does not support base16
Merge pull request #784 from hintjens/master

Problem: zbeacon does not recover from network changes
Problem: Can't install with out of tree build

Solution: Make was searching for czmq.7 file in srcdir while in fact it
is created during compilation, so removing the srcdir reference to let
it proceed.
Merge pull request #788 from miska/master

Problem: Can't install with out of tree build
Added base32 to zarmour.
Added linebreak properties to zarmour.
Added mode_str method to zarmour.
Cleaned up zarmour code.
Problem: No builtin way to build for qt-android
Solution: Add qt-android build system and add to travis-ci
Problem: ci_build.sh is not executable
Solution: Change its permissions to make it executable
Problem: qt-android build does not fetch dependencies
Solution: clone libzmq in builds/qt-android/ci_build.sh
Changes addressing #787.
Merge pull request #789 from jemc/builds-qt-android

Problem: No builtin way to build for qt-android
Merge pull request #790 from pmienk/master

Changes addressing #787.
Problem: impossible to get at keys of key/value pairs in a zing

Solution: provide zring_key() method:

//  Return the key of the current item in the ring. If the ring is empty, or the
//  cursor passed the end of the ring, returns NULL. Does not change the cursor.
CZMQ_EXPORT const void * zring_key (zring_t *self);
Merge pull request #791 from skaes/add_zring_key_method

Problem: impossible to get at keys of key/value pairs in a zring
fixed that zring tests wouldn't compile on ubuntu
Merge pull request #792 from skaes/add-missing-casts

fixed that zring tests wouldn't compile on ubuntu