Add note to PayPal configuration that PayPal Sandbox is hit-or-miss

[raamdev]

Many people have trouble testing s2Member with the PayPal Sandbox and we always suggest doing Live $0.01 transactions instead.

We should mention somewhere in the s2Member PayPal configuration (where you can enable PayPal Sandbox mode) that Sandbox mode is often hit-or-miss and that we recommend running Live tests with $0.01 transactions for more accurate testing and real-world simulation.

[jaswrks]

Next Release Changelog:

• (s2Member/s2Member Pro) PayPal Sandbox: This release updates the inline documentation under the PayPal Account Settings section of s2Member. We now suggest that instead of enabling PayPal Sandbox Mode (sometimes buggy at best), that site owners run tests with low-dollar amounts against a live PayPal account instead; e.g., $0.01 test transactions in live mode work great also. See this GitHub issue if you'd like additional details. Props @raamdev for mentioning this again.

[jaswrks]

s2Member & s2Member Pro v160423 have been released and they include changes from this GitHub Issue. See the v160423 announcement for further details.

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This issue will now be locked to further updates. If you have something to add related to this GitHub Issue, please open a new GitHub Issue and reference this one. Thanks! :-)