Fix arrays merge

[IgorFedchenko]

Close #137

While debugging, it turned out that what current implementation does is taking value by key (create if not exists) and append array values to it.

So, actually, the following:

c: {
    a: [2. 3]
    b: [4]
    a: [5]
}

was ending up with a = [2, 3, 5]. So, arrays with same paths were always concatenating, as if one was continuation of another.

And as far as I understand the specs, the only case when arrays are concatenated is when they are separated with non-newline while space. From README:

Within an field value or array element, if only non-newline white-space separates the end of a first array or object or substitution from the start of a second array or object or substitution, the two values are concatenated.

So for me, this is a special case that should be explicitly handled. Like when you have ] token, check if next tokens are some white-spaces and then [ token - and in that case just skip this part and keep going.

So, that is what basically my fix is doing:

1. When we find second key with same path (i.e. second a) and there is already existing array, do not concatenate them (I am calling Clear on old value)
2. When during array parsing we have a special case described above, do the "special thing"

[IgorFedchenko]

Added this to verify that array merging still works