add discrete-time laguerre basis for identification

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.07 :tada:

Comparison is base (63b375b) 86.44% compared to head (c5c48dc) 86.52%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #119 +/- ## ========================================== + Coverage 86.44% 86.52% +0.07% ========================================== Files 12 12 Lines 2140 2152 +12 ========================================== + Hits 1850 1862 +12 Misses 290 290 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `86.52% <100.00%> (+0.07%)` | :arrow_up: | 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=Fredrik+Bagge+Carlson#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/baggepinnen/ControlSystemIdentification.jl/pull/119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fredrik+Bagge+Carlson) | Coverage Δ | | |---|---|---| | [src/ControlSystemIdentification.jl](https://codecov.io/gh/baggepinnen/ControlSystemIdentification.jl/pull/119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fredrik+Bagge+Carlson#diff-c3JjL0NvbnRyb2xTeXN0ZW1JZGVudGlmaWNhdGlvbi5qbA==) | `81.04% <ø> (ø)` | | | [src/basis\_functions.jl](https://codecov.io/gh/baggepinnen/ControlSystemIdentification.jl/pull/119?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fredrik+Bagge+Carlson#diff-c3JjL2Jhc2lzX2Z1bmN0aW9ucy5qbA==) | `88.72% <100.00%> (+1.11%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fredrik+Bagge+Carlson). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fredrik+Bagge+Carlson)

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