Better handling of optional arguments

[Sov-trotter]

closes #10, #12 & #11

we can have a Qobj specific block here (say Experiment{N} <: AbstractBlock{N}), that takes a ChainBlock and a config and header, then accept a list of them and lower them to Qobj.

This wasn't needed since multiple dispatch made things easier.

Also I had to use @options from IBMQClient to get around this error

[codecov]

Codecov Report

Merging #13 (7b448d4) into main (c281f47) will increase coverage by 8.92%.
The diff coverage is 82.22%.

@@            Coverage Diff             @@
##             main      #13      +/-   ##
==========================================
+ Coverage   75.00%   83.92%   +8.92%     
==========================================
  Files           1        2       +1     
  Lines          52      112      +60     
==========================================
+ Hits           39       94      +55     
- Misses         13       18       +5     

Impacted Files	Coverage Δ
src/qbir.jl	81.69% <81.69%> (ø)
src/qobj.jl	87.80% <84.21%> (+12.80%)	⬆️

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[Roger-luo]

FYI. that should be an error at least before 2.0, you must use things Configurations to have the keyword struct syntax. And for web applications, it is usually to use things like Configurations to define a schema for security reason.

[Roger-luo]

also please remember to format the doc strings. For this part you have to do it manually, run JuliaFormatter in this PR before we merge things would also be a good idea.

[Roger-luo]

let's have some more tests to push the covarage above 80% at least.

[Roger-luo]

nice work! thanks