[WIP] Rewrite the whole thing based on a high-accuracy epoch type

[helgee]

I got started with a new accuracy-preserving type. The design is based on the AbsoluteDate class from Orekit: https://github.com/CS-SI/Orekit/blob/develop/src/main/java/org/orekit/time/AbsoluteDate.java

EDIT: This is basically a straight port of Orekit's time package. Imitation is the sincerest form of flattery 😉

CC: @bgodard, @giordano, @prakharcode

ToDo

• [x] String I/O
• [x] Periods & comparisons
• [x] Leap seconds
• [x] Ranges
• [ ] Lots of tests
• [x] Remove old code
• [ ] Docs

[codecov-io]

Codecov Report

Merging #43 into master will increase coverage by 4.92%. The diff coverage is 89.84%.

@@            Coverage Diff            @@
##           master     #43      +/-   ##
=========================================
+ Coverage   87.38%   92.3%   +4.92%     
=========================================
  Files           7       7              
  Lines         539     169     -370     
=========================================
- Hits          471     156     -315     
+ Misses         68      13      -55

Impacted Files	Coverage Δ
src/Periods.jl	100% <ø> (+13.04%)	:arrow_up:
src/offsets.jl	100% <100%> (ø)
src/leapseconds.jl	100% <100%> (ø)
src/AstroTime.jl	100% <100%> (ø)	:arrow_up:
src/accessors.jl	75% <75%> (ø)
src/AstroDates.jl	85.24% <85.24%> (ø)
src/Epochs.jl	94.73% <94.73%> (-2.41%)	:arrow_down:
... and 2 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update d82fc87...e33f310. Read the comment docs.

[helgee]

@giordano Do you happen to know how one overloads the colon operator?

[giordano]

It used to be lowered to the colon function in previous versions, now it should be lowered to a function called : according to the release notes.

[helgee]

...and we have ranges 🎉