Added unixtimestamps support for date parser

[rmarku]

I base this PR in #48 as I wanted to remove the fmt.Print statement too (#48 should be merged first).

This PR add support to Unix timestamp dates in the getParsedDate function. Before fail, it tries to convert the date string to an integer and then get the time.Time from its Unix time representation.

There could be some more test to verify this number represented in a string is not something else, like a date range maybe?

Added a test page where I found this timestamp thing.

[fmartingr]

Hey @rmarku, thank you for the contribution! This seems like a useful addition. Im worried about spending too much parsing time in this function but it is what it is.
Let's wait until we settle up in #48 and then we are good to go.