Convert normal date to Julian Date

This function takes a vector of dates and derives Julian Date out of it.

This function is different from Matlab's built-in functions (juliandate or mjuliandate) in the sense
that it gives yyyyddd where yyyy is the year and ddd is the day out of
365 (or 366 for leap years).
The output is a float with 7 significant numbers for yyyyddd and floating point numbers for time (if the given date does contain time).