Added a schema for products

[mak001]

discussed in #39

[codecov]

Codecov Report

Merging #100 (45d2674) into master (280eab2) will decrease coverage by 0.40%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #100      +/-   ##
============================================
- Coverage     14.89%   14.49%   -0.41%     
- Complexity      273      282       +9     
============================================
  Files            15       16       +1     
  Lines           933      959      +26     
============================================
  Hits            139      139              
- Misses          794      820      +26     

Flag	Coverage Δ
unittests	14.49% <0.00%> (-0.41%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/Client/ShopifyClient.php	0.00% <0.00%> (ø)
src/Page/ShopifyProduct.php	60.75% <ø> (ø)
src/SEO/ProductSchemaBuilder.php	0.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 280eab2...45d2674. Read the comment docs.