vec2: Add near() operator

We want to know if two vectors are within a specified epsilon of each
other, instead of being equal.
vec3: Add near() operator

Similar to the one we added to vec2.
vec4: Add near() operator

Similar to the one we added to vec2 and vec3.
vectors: Allow fuzzyness in equality checks

We should allow for floating point representation discrepancies when
checking two vectors for equality. The immediate check using the SIMD
comparison operator has the same issue as a direct equality using
memcmp() or '==', but also we want to check within an arbitrary high
precision.

We use the same strategy (and epsilon) to check if two graphene_point_t
or two graphene_point3d_t are equal as well.
tests: Use near() operator in fuzzy vector comparison macros

We have this new operator for vector types, so we should use it to
simplify the macro expansion.