added support for saving with a QuoteMode

[tobithiel]

I'm dealing with some messy csv files and being able to just quote all fields is very useful, so that other applications don't misunderstand the file because of some sketchy characters.
This also enables disabling quoting all together, which would resolve #119, and only quoting non-numeric fields.

[codecov-io]

Current coverage is 86.18%

Merging #254 into master will increase coverage by +0.11% as of 765ffc9

@@            master    #254   diff @@
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  Files           12      12       
  Stmts          517     521     +4
  Branches       149     151     +2
  Methods          0       0       
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+ Hit            445     449     +4
  Partial          0       0       
  Missed          72      72       

Review entire Coverage Diff as of 765ffc9

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[HyukjinKwon]

Hm.. Does this really check if the output is quoted or not?

[tobithiel]

Not sure why it's not rerunning the tests, but I pushed extended tests. I'm not that familiar with Scala, so please feel free to write that in a more elegant way.
Most of the other tests writing csv files don't check what's actually in the file as well, so these kind of checks should probably extended to these tests as well.

[tobithiel]

@HyukjinKwon Are you interested in merging this in? Do you have more feedback?

[HyukjinKwon]

@tobithiel I do not have the permission. cc @falaki

[falaki]

@tobithiel This is a cool feature to have in spark-csv. Would you make sure it works with the other parse mode as well?

[tobithiel]

@falaki I'm not sure I get what you mean? This only deals with writing files and since parsing csv files with quotes is already tested & works, parsing the written files again works out of the box.

[falaki]

@tobithiel Thanks. This looks good.