Hosting configuration was made consistent

[pakrym]

We made hosting configuration keys to be consistent in command line/environment variables/hosting.json. Also Microsoft.AspNet.Hosting.json configuration file was renamed to hosting.json

Issue:
aspnet/Hosting#453

Related
#94

Old Key	New Key	Description
server or Hosting:Server	Environment Variable: ASPNET_SERVER hosting.json: server Command Line: --server	Specifies which server to use
app or Hosting:App	Environment Variable: ASPNET_APP hosting.json: app Command Line: --app	assembly containing startup class
ASPNET_ENV or Hosting:Environment	Environment Variable: ASPNET_ENVIRONMENT or ASPNET_ENV (obsolete) hosting.json: environment Command Line: --environment	The environment to run as (Development, Production etc.)
webroot	Environment Variable: ASPNET_WEBROOT hosting.json: webroot Command Line: --webroot	Webserver root, used by IIS and static file servers
Hosting:DetailedErrors	Environment Variable: ASPNET_DETAILEDERRORS hosting.json: detailedErrors Command Line: --detailedErrors	Show detailed errors for startup failures

Sample Configuration File

{
   "webroot": "wwwroot",
   "server" : "Microsoft.AspNet.Server.Kestrel",
   "app": "MyProjectReference",
   "environment": "Development",
   "detailedErrors": true
}

Sample Environment Variables:
All environment variables are prefixed with ASPNET_ prefix.

ASPNET_WEBROOT=wwwroot
ASPNET_SERVER=Microsoft.AspNet.Server.Kestrel
ASPNET_APP=MyProjectReference
ASPNET_ENVIRONMENT=Development
ASPNET_DETAILEDERRORS=true

Sample Command line:

Microsoft.AspNet.Hosting --server Microsoft.AspNet.Server.Kestrel --webroot "wwwroot" --app "MyProjectReference" --environment "Development" --detailedErrors true

[Tratcher]

Note these environment variables have been updated to ASPNETCORE_ as described in #144 (comment).