Update os specific verifier constant path (#94)

This commit makes the following changes :
- verfier_constants path from posix path to os specific path check, which helps in valid request verification in other than posix os. 
- default timestamp tolerance value from 30 seconds to 150 seconds.
- The docstring links to the right documentation on developer docs.

Thanks @JACTheCreator for raising #89 to get this to our attention.

Author: nikhilym

ask-sdk-webservice-support/ask_sdk_webservice_support/verifier_constants.py

@@ -15,44 +15,45 @@
 # specific language governing permissions and limitations under the
 # License.
 #
+import os
 
 #: Header key to be used, to retrieve request header that contains the
 #: URL for the certificate chain needed to verify the request signature.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#checking-the-signature-of-the-request>`__.
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-signature>`__.
 SIGNATURE_CERT_CHAIN_URL_HEADER = "SignatureCertChainUrl"
 
 #: Header key to be used, to retrieve request header that contains the
 #: request signature.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#checking-the-signature-of-the-request>`__.
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-signature>`__.
 SIGNATURE_HEADER = "Signature"
 
 #: Case insensitive protocol to be checked on signature certificate url.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#cert-verify-signature-certificate-url>`__.
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-signature>`__.
 CERT_CHAIN_URL_PROTOCOL = "https"
 
 #: Case insensitive hostname to be checked on signature certificate url.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#cert-verify-signature-certificate-url>`__.
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-signature>`__.
 CERT_CHAIN_URL_HOSTNAME = "s3.amazonaws.com"
 
 #: Path presence to be checked on signature certificate url.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#cert-verify-signature-certificate-url>`__.
-CERT_CHAIN_URL_STARTPATH = "/echo.api/"
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-signature>`__.
+CERT_CHAIN_URL_STARTPATH = "{0}echo.api{0}".format(os.path.sep)
 
 #: Port to be checked on signature certificate url.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#cert-verify-signature-certificate-url>`__.
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-signature>`__.
 CERT_CHAIN_URL_PORT = 443
 
 #: Domain presence check in Subject Alternative Names (SANs) of
 #: signing certificate.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#checking-the-signature-of-the-request>`__.
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-signature>`__.
 CERT_CHAIN_DOMAIN = "echo-api.amazon.com"
 
 #: Character encoding used in the request.
 CHARACTER_ENCODING = "utf-8"
 
 #: Default allowable tolerance in request timestamp.
-#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#timestamp>`__.
-DEFAULT_TIMESTAMP_TOLERANCE_IN_MILLIS = 30000
+#: For more info, check `link <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html#check-request-timestamp>`__.
+DEFAULT_TIMESTAMP_TOLERANCE_IN_MILLIS = 150000
 
 #: Maximum allowable tolerance in request timestamp.
 #: For more info, check `link <https://developer.amazon.com/docs/smapi/skill-events-in-alexa-skills.html#delivery-of-events-to-the-skill>`__.