fix for trimmed quoted separators

[dejan1024]

This is a fix for the following issue:
Sample document:

first, second
"yes", ", but"

Note the space after the separator. When loading this file (with pTrim = true and pAutoQuote = true), the second column will be read as only "\"", the comma after it will be interpreted as another separator.

The cause is in rapidcsv.h:1587:

if (cell.empty() || (cell[0] == mSeparatorParams.mQuoteChar))
{
    quoted = !quoted;
}

which does not trigger when there is whitespace before the opening quote.

This PR allows for whitespace in front of the first quote when trimming is enabled.

[d99kris]

Hi @dejan1024 - thanks for contributing!
I believe the use-case makes sense for rapidcsv to handle. I'll try find some time to review the patch properly soonish and get it merged.

[d99kris]

Thanks again for contributing @dejan1024, the fix has been integrated now. I just added a test case, bumped version and did some minor code formatting fixes.