Added datasource Bank of England database

[dwinrow]

No description provided.

[codecov]

Codecov Report

Merging #85 (cbaa9a4) into master (cbeb769) will decrease coverage by 2.85%.
The diff coverage is 84.61%.

❗ Current head cbaa9a4 differs from pull request most recent head f49adfa. Consider uploading reports for the commit f49adfa to get more accurate results

@@            Coverage Diff             @@
##           master      #85      +/-   ##
==========================================
- Coverage   93.10%   90.24%   -2.86%     
==========================================
  Files           4        4              
  Lines          58       82      +24     
==========================================
+ Hits           54       74      +20     
- Misses          4        8       +4     

Impacted Files	Coverage Δ
src/MarketData.jl	100.00% <ø> (ø)
src/downloads.jl	89.47% <84.61%> (-2.84%)	⬇️

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[Arkoniak]

Usually we use CamelCase for modules and type names, not for fields.
Can we switch to lowercase? Like

struct BoeOpt
    date_from::Date
    date_to::Date
    using_codes::Bool
    csvf::String
    vpd::Bool
end

[dwinrow]

An AbstractQueryOpt is passed to the HTTP GET command with its fieldnames and values as a query.

I chose fieldnames to be consistent with the API documentation. https://www.bankofengland.co.uk/boeapps/database/Help.asp#CSV

However, I agree that lowercase is standard for fieldnames, and since the parameter names in a HTTP GET query are case-insensitive this shouldn't cause an issue. However, underscores would not be consistent with AbstractQueryOpt as I would need to change the field names to construct the query.

[Arkoniak]

There was an error

BOE: Test Failed at /home/travis/build/JuliaQuant/MarketData.jl/test/downloads.jl:31
Expression: boe("asdfasdf")
Expected: APIError
Thrown: UndefVarError