update correlate

[ahmadtourei]

Description

This PR adds four new capabilities to the correlate function:

• [x] patch can be in the frequency domain, thereby eliminating the need for the Fourier transform step.
• [x] keeps the patch in the frequency domain after computing the correlation if the idft argument is set to False.
• [x] an step_size argument to skip receivers.
• [ ] compute correlation over an array of master sources (passed as kwargs) instead of one master source, which results in a 3D patch.

Checklist

I have (if applicable):

• [x] referenced the GitHub issue this PR closes.
• [x] documented the new feature with docstrings or appropriate doc page.
• [x] included a test. See testing guidelines.
• [x] your name has been added to the contributors page (docs/contributors.md).
• [ ] added the "ready_for_review" tag once the PR is ready to be reviewed.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 99.51%. Comparing base (8e93570) to head (c4d5542).

Files	Patch %	Lines
dascore/proc/correlate.py	96.61%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #364 +/- ## ========================================== - Coverage 99.53% 99.51% -0.03% ========================================== Files 97 97 Lines 7596 7635 +39 ========================================== + Hits 7561 7598 +37 - Misses 35 37 +2 ``` | [Flag](https://app.codecov.io/gh/DASDAE/dascore/pull/364/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/DASDAE/dascore/pull/364/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE) | `99.51% <96.66%> (-0.03%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE#carryforward-flags-in-the-pull-request-comment) to find out more.

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[d-chambers]

closed by #400