WIP: Implement vagus nerve stimulation (VNS) tracking

[ericoc]

Working on creating an Alexa intent and subsequent voice command such as "Alexa, tell seizure tracker to track VNS" (or similar wording, something with "VNS" anyways).

The add_vns function I've started working on should tie a VNS "swipe" to the latest seizure event returned by my get_latest_seizure function (i.e. the most recent seizure on SeizureTracker.com that does not have an end date).

For those curious about the medicine, a "VNS swipe" is the act of a human swiping a special magnet across a titanium implant (known as a Vagus nerve stimulator) implanted in the chest wall of someone with epilepsy to activate electrical impulses: https://en.wikipedia.org/wiki/Vagus_nerve_stimulation

[ericoc]

There are seven (7) items that exist within a seizure/event object when communicating with the SeizureTracker.com API:

Name	Values
VNSProfileDate_Active	Yes or NULL
VNS_MagnetUsed	Yes, No / when usage attached to events, defaults to Yes
VNS_UsedBy	Patient, Caregiver, Family Member, Other
VNS_NumTimesUsed	1 - 99
VNS_StoppedSeizure	Yes, No
VNS_DecreasedIntensity	Yes, Moderately, No
VNS_DecreasedAfterEffects	Yes, Moderately, No

Additionally, it seems any of these can also have an empty (string) value.

Mostly, I need to determine the correct default values for these VNS values when adding a new seizure in the add_seizure function (regardless of whether $new_seizure is created from the get_latest_seizure function or the base object in seizure.object.php).

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Other questions:

• Should it do math on VNSNumTimesUsed by adding one (+1) each time the add_vns function runs against an individual seizure GUID?
• If VNSProfileDate_Active is Yes on the latest seizure, when adding a seizure, should Alexa ask if VNS was used? Probably not.
• Create a count_vns function similar to the count_seizures function? Maybe eventually?