feat: handle single-type entity type

[benjamincanac]

Handle Single Type endpoints: https://strapi.io/documentation/v3.x/content-api/api-endpoints.html#endpoints

• update and delete methods now works without the id
• Entities can now be defined like:

entities: [
  'products',
  { name: 'articles', type: 'collection' },
  { name: 'homepage', type: 'single' }
]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[codecov]

Codecov Report

Merging #35 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master       #35   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           13        13           
  Branches         3         3           
=========================================
  Hits            13        13           

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[atinux]

Can you update the docs? 😀

[atinux]

What about supporting single:homepage since the entities cannot have : in their names?