Add rounding for date parser

[Paxa]

To avoid float precision mistake, e.g. 42988.99999999999 (11 September 2017) should be parsed same as 42989.0 to match with date time parser and excel behaviour

Fixes #500

[coveralls]

Coverage increased (+0.04%) to 94.403% when pulling e6da217 on Paxa:master into 4ec1104 on roo-rb:master.

[Paxa]

Found some strange behaviour of ruby Date object:
if we create Date with fractional part then it will be often ignored but not always:

d = Date.new(2017, 9, 11) + 15/24r
# d => #<Date: 2017-09-11 ((2458008j,54000s,0n),+0s,2299161j)>
#                                     ^ fractional part, 54,000 seconds
# in rails it will be printed as "Mon, 11 Sep 2017"

# no time info
d.to_time # => 2017-09-11 00:00:00 +0800
d.to_datetime # => #<DateTime: 2017-09-11T00:00:00+00:00 ((2458008j,0s,0n),+0s,2299161j)>
d == Date.parse("Mon, 11 Sep 2017") # => false (difficult to understand reason)

# has time info
d.strftime("%F %T %z") # => "2017-09-11 15:00:00 +0000"
d.day_fraction # => (5/8)

Imo it's difficult to understand that date may have fractional part, especially in rails
Probably should not use fraction part for date values

What do you think?

[chopraanmol1]

Thank you for opening this PR. Can you add a relevant test case for this? Adding test case will ensure that this case is covered in the future as well.

[chopraanmol1]

LGTM. Can you add a relevant test case to cover this scenario?

[Paxa]

Sorry, I'm not familiar with your testing setup

[Paxa]

Could you give a hint on how to make tests?