Fix for #42

Rename Market\MarketClient

Market\MarketClient moved to sub-namespace called Partner and renamed according to common package naming practice to PartnerClient
So now the fully-qualified class name will be Market\Partner\PartnerClient
Merge pull request #57 from tankist/market-partner

Fix for #42
Merge pull request #3 from nixsolutions/master

Update
Added state parameter in auth request
Merge pull request #58 from naxel/master

Added state parameter in auth request
Changed in AuthRequestException message
Merge pull request #59 from naxel/master

Changed in AuthRequestException message
Added Market Content API client skeleton