Convert marked array entity into actual array object.

[blackwinter]

The last commit (7d9b2a4) might be debatable; but I feel making intentions explicit works in our favor for now (the usual WDCD applies, though).

Note that I deliberately went in the direction of more explicit types instead of less:

TODO? maybe this would be a good general internal representation, resulting
in every value being either a hash or a string, no more separate array type.

Resolves #109 and fixes most of the array issues in #100 (see 11d1e71).

[fsteeg]

(Note to self & @TobiasNx: we'll probably have to add some set_array statements in OERSI & Playground samples when we deploy this.)

[TobiasNx]

(Note to self & @TobiasNx: we'll probably have to add some set_array statements in OERSI & Playground samples when we deploy this.)

@blackwinter & @fsteeg.
Does this mean new created fields cannot be part of an array unless the array already exists?
e.g.:
add_field("ab.$append", "abc")

move_field("xy", "qr.$append.cd")

Is this conceptually not possible or just not realised yet?

[blackwinter]

Does this mean new created fields cannot be part of an array unless the array already exists?

Exactly.

Is this conceptually not possible or just not realised yet?

Intentionally not implemented (yet). Catmandu supports it, though, so maybe we should too?