CMake: add more warning flags
Merge pull request #201 from toxeus/moreWarnings

CMake: add more warning flags
OTAPI_Exec: fix -Wlogical-op

Logical ‘and’ of mutually exclusive tests is always false.
Merge pull request #202 from toxeus/fixLogicalOP

OTAPI_Exec: fix -Wlogical-op
git: improve pre-push hook error message
Merge pull request #204 from toxeus/improveMsg

git: improve pre-push hook error message
Updates build instructions.

Adds g++ and ZMQ.