Declare the graph mutex.
Macros to abstract returning from a function holding locks.
Link with a bunch of necessary libraries
Moved required libraries into a variable
Graph public functions lock
Renamed graph_lock to mutex
Implemented thread safety for nodes

Note that there are a few places where it's not, but that these need implementation anyway.
Refactored and rolled out more thread safety:

- Macros LOCK, STANDARD_CLEANUP_BLOCK, WILL_RETURN implement it.
- TO use the error condition macros, you must use at least WILL_RETURN.
- See private_macros.h
Thread safety for sineNode.