Creating constructiors for ready objects.

[marcpaterno]

This PR will be a step towards one-phase construction of Statistics and contained objects. This will eventually allow us to remove the read step, and thus simplify the construction of likelihoods.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.8%. Comparing base (221cf65) to head (bcd54a5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #399 +/- ## ======================================== + Coverage 95.5% 97.8% +2.3% ======================================== Files 34 35 +1 Lines 2569 2989 +420 ======================================== + Hits 2454 2926 +472 + Misses 115 63 -52 ``` | [Files](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC) | Coverage Δ | | |---|---|---| | [firecrown/connector/cosmosis/likelihood.py](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?src=pr&el=tree&filepath=firecrown%2Fconnector%2Fcosmosis%2Flikelihood.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-ZmlyZWNyb3duL2Nvbm5lY3Rvci9jb3Ntb3Npcy9saWtlbGlob29kLnB5) | `97.0% <100.0%> (+5.0%)` | :arrow_up: | | [...ood/gauss\_family/statistic/source/number\_counts.py](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?src=pr&el=tree&filepath=firecrown%2Flikelihood%2Fgauss_family%2Fstatistic%2Fsource%2Fnumber_counts.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-ZmlyZWNyb3duL2xpa2VsaWhvb2QvZ2F1c3NfZmFtaWx5L3N0YXRpc3RpYy9zb3VyY2UvbnVtYmVyX2NvdW50cy5weQ==) | `83.8% <100.0%> (+5.1%)` | :arrow_up: | | [...likelihood/gauss\_family/statistic/source/source.py](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?src=pr&el=tree&filepath=firecrown%2Flikelihood%2Fgauss_family%2Fstatistic%2Fsource%2Fsource.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-ZmlyZWNyb3duL2xpa2VsaWhvb2QvZ2F1c3NfZmFtaWx5L3N0YXRpc3RpYy9zb3VyY2Uvc291cmNlLnB5) | `100.0% <ø> (ø)` | | | [...hood/gauss\_family/statistic/source/weak\_lensing.py](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?src=pr&el=tree&filepath=firecrown%2Flikelihood%2Fgauss_family%2Fstatistic%2Fsource%2Fweak_lensing.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-ZmlyZWNyb3duL2xpa2VsaWhvb2QvZ2F1c3NfZmFtaWx5L3N0YXRpc3RpYy9zb3VyY2Uvd2Vha19sZW5zaW5nLnB5) | `92.7% <100.0%> (+7.5%)` | :arrow_up: | | [...own/likelihood/gauss\_family/statistic/two\_point.py](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?src=pr&el=tree&filepath=firecrown%2Flikelihood%2Fgauss_family%2Fstatistic%2Ftwo_point.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-ZmlyZWNyb3duL2xpa2VsaWhvb2QvZ2F1c3NfZmFtaWx5L3N0YXRpc3RpYy90d29fcG9pbnQucHk=) | `96.8% <100.0%> (+20.6%)` | :arrow_up: | | [firecrown/metadata/two\_point.py](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?src=pr&el=tree&filepath=firecrown%2Fmetadata%2Ftwo_point.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-ZmlyZWNyb3duL21ldGFkYXRhL3R3b19wb2ludC5weQ==) | `100.0% <100.0%> (ø)` | | | [firecrown/utils.py](https://app.codecov.io/gh/LSSTDESC/firecrown/pull/399?src=pr&el=tree&filepath=firecrown%2Futils.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-ZmlyZWNyb3duL3V0aWxzLnB5) | `100.0% <100.0%> (ø)` | |