Added more fields

Added applicationName as a parameter to the constructor and userAgent, applicationName as fields of the JSON logs.
applicationName as Optional

Made applicationName in the constructor as optional to maintain backward compatibility. If applicationName is not passed by the user then default value will be "loggly-csharp-app"
Added an extra constructor

Added constructor that can only receive inputKey and applicationName as parameters. Now we are not forced to pass null for the alternativeUrl to pass applicationName in the previous constructor.
Added Constructor chaining

To minimize business logic, forwarded public Logger(string inputKey,string applicationName)value to  public Logger(string inputKey, string alternativeUrl = null, string applicationName = null )
Merge pull request #14 from psquickitjayant/master

Update to loggly-csharp library