v3.0.0b1

Added in 3.0.0b1:

• Webargs 8 support (@pzhang65) - #112
• apispec 5 support (@kiforchuk) - #115

Changes compared to 2.2.1 version:

• Update swagger-ui static files to version 4.1.0 (@slymit) - 727d2c1
• Fixes response validation error when description is not provided (@mat-work) - e96db8b
• Relative url param (Artur Gwiazda) - 0ebdc86
• Added url_for usage to support nested apps (@AivanF) - 0c72d94
• Add custom schema name resolver for MarshmallowPlugin (@va-dev) - ba786ba
• Described in README semver is supported (@alvassin) - ef6c215
• Pass example to request schema (@Niccolum) - #90