Unclear documentation for link types

[samuelhorwitz]

Describe the bug
Visiting the Go docs on Link Type, you'll see that the comments are as follows:

const (
    LinkTypeUnspecified LinkType = iota // The relationship of the two spans is unknown.
    LinkTypeChild                       // The current span is a child of the linked span.
    LinkTypeParent                      // The current span is the parent of the linked span.
)

However, I couldn't tell if this was correct looking at how Stackdriver displays it (the wording is strange, it's vague and makes it seem as though using LinkTypeChild presents the linked span as a child of the current). I decided to take a look at some other library docs, and in the Java documentation it appears the definition is the opposite:

CHILD_LINKED_SPAN
When the linked Span is a child of the current Span.

PARENT_LINKED_SPAN
When the linked Span is a parent of the current Span.

To Reproduce
See my above documentation links

Expected behavior
Clarity needed on what is correct, expected behavior shouldn't actually change code-wise, only what choice should be made by the developer

Additional context
N/A

[rghetia]

@samuelhorwitz Java definition is correct. i'll fix the go definition.

[songy23]

Fixed with #1062.