IO bomb:

[argonaut22]

• added quicksaves and quickloads of aircraft
• added save_model to save to output readable toml's a la read_input
• edited read_input to handle multi-mission and multi-point specs
• added par_array_operations.jl for convenient array manipulations (e.g., array2nestedvector())
• added convenience aircraft import fxn's, read_mdl() and read_jl() in read_externals.jl
• added output_csv(). able to specify flight points, missions, par_array indices, to be written to csv. has logic for appending multiple aircraft to a single csv if outputs are consistent.
• added field to aircraft struct: sized = [true/false] as a sizing flag
• docstrings throughout (doc page and examples forthcoming)
• misc bugs and tweaks

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 82.41431% with 118 lines in your changes are missing coverage. Please review.

Project coverage is 73.84%. Comparing base (ffe41de) to head (5c6ee55).

Files	Patch %	Lines
src/IO/save_model.jl	80.52%	82 Missing :warning:
src/IO/output_csv.jl	80.26%	15 Missing :warning:
src/IO/read_externals.jl	0.00%	13 Missing :warning:
src/IO/par_array_opers.jl	86.95%	6 Missing :warning:
src/IO/quicksave_load.jl	96.87%	1 Missing :warning:
src/IO/read_input.jl	98.70%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #20 +/- ## ========================================== + Coverage 73.10% 73.84% +0.74% ========================================== Files 64 68 +4 Lines 12373 12906 +533 ========================================== + Hits 9045 9531 +486 - Misses 3328 3375 +47 ```

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[askprash]

@argonaut22 I just pulled in another PR #18 which have caused a few merge conflicts. Could you please resolve these?