Add image extraction options

[adrg]

• Add options to ExtractPageImages extractor method
• Skip extraction of inline stencil masks by default

Resolves #362

[codecov]

Codecov Report

Merging #363 into v3 will increase coverage by 5.37%.
The diff coverage is 62.5%.

@@            Coverage Diff            @@
##               v3    #363      +/-   ##
=========================================
+ Coverage   55.22%   60.6%   +5.37%     
=========================================
  Files         151     151              
  Lines       27218   27224       +6     
=========================================
+ Hits        15031   16498    +1467     
+ Misses      10341   10339       -2     
+ Partials     1846     387    -1459

Impacted Files	Coverage Δ
pdf/extractor/image.go	79.13% <62.5%> (+12.15%)	⬆️
pdf/annotator/field_appearance.go	11.5% <0%> (+0.62%)	⬆️
pdf/creator/division.go	89.13% <0%> (+1.08%)	⬆️
pdf/model/outline.go	86.74% <0%> (+1.2%)	⬆️
pdf/creator/invoice.go	90.07% <0%> (+1.21%)	⬆️
pdf/model/sighandler/sighandler_rsa_sha1.go	6.75% <0%> (+1.35%)	⬆️
pdf/annotator/form_field.go	15% <0%> (+1.42%)	⬆️
pdf/model/annotations.go	23.08% <0%> (+1.48%)	⬆️
pdf/creator/toc_line.go	75.39% <0%> (+1.58%)	⬆️
pdf/creator/chapters.go	79.64% <0%> (+1.76%)	⬆️
... and 94 more

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[gunnsth]

Looks good, one minor change needed.

[gunnsth]

Let's use "Options" rather than "Opts" for consistency (Options used in elsewhere in unidoc).

[adrg]

Done