Make readtable()'s "quotemark" argument a vector, remove "allowquotes"

Making "quotemark" a vector allows quite naturally to choose several
quoting characters (potentially useful for some weird files), and
disabling the use of quoting altogether by passing an empty vector.
This simple implementation does not take into account a possible
nesting of two different types of quote marks. This allows keeping
the performance impact low. Cf. issue #400.
Merge pull request #401 from nalimilan/quotemarks

Make readtable()'s "quotemark" argument a vector, remove "allowquotes"
Finished purge of DataArrays code. show(df) still fails
join() is broken
Merge pull request #403 from JuliaStats/purge

Remove DataArrays
REQUIRE: add dependency on DataArrays
Merge pull request #410 from StefanKarpinski/patch-2

REQUIRE: add dependency on DataArrays
Fix failing test due to quotes handling

Introduced by 7d4c9e53497bd5f0bf1594677d9be8021a1379de. 'in' does
not consider that a Uint8 is in a Vector{Char}, we need to convert
to a Vector{Uint8} first.

Also stop passing 'o.quotemark' to bytestostring() since it is not
used.