JSON parsing, applied to pvxput

[mdavidsaver]

Wrap YAJL parser from Base, which requires Base >=3.15. Teach pvxput to make use of this.

Adds special case handling of enum_t at a low level through the Struct node.

Relaxes requirement to prefix Union member access with -> at the beginning of an expression.

TODO:

• Assign Any by inferring a TypeDef.
• Handle uint64

[mdavidsaver]

@klemenv wrt. #3 are you still using PVXS with Base 3.14?

[AppVeyorBot]

✅ Build pvxs 1.0.982 completed (commit e246b1680b by @mdavidsaver)

[mdavidsaver]

My recent addition of ABI diff to GHA (de12bc1) turns up the following, which I can replicate locally. I am not sure what to make of it. Why would this non-inline function apparently not follow the Linux/amd64 calling convention?

pvxs/src/pvxs/data.h

Lines 605 to 609 in 2dcdb85

	// use with caution
	void copyOut(void *ptr, StoreType type) const;
	bool tryCopyOut(void *ptr, StoreType type) const;
	void copyIn(const void *ptr, StoreType type);
	bool tryCopyIn(const void *ptr, StoreType type);