Allow use of "value decorators" (like `[` and `]` for arrays) for reading `CsvSchema` columns

[cowtowncoder]

Currently it is possible to decode Array values from columns, by specifying Array Element separator (default being ";"). But there is quite a bit of data that uses outer "wrappers", f.ex commonly we might have:

id,title,"[1.0, 0.4, 16.98]"

wherein brackets are used around the sequence of values.

We should allow supporting such notation by addition to CsvSchema. Could start by allowing use of start/end String; no need to get fancy at first (but could conceivably support regexps if need be, i.e. take java.util.regex.Pattern start/end markers).

NOTE: this issue is specifically for READING such decorated values: different issue (#495) filed for WRITING.

[cowtowncoder]

Changing definition so that CsvValueDecorators can be registered for actual columns.
And in fact initially that is how it must be done, assigning to specific columns.
After this works, may consider per-schema Array decorators.