Add MySQLPlugin to plugins

[tom-pytel]

No description provided.

[kezhenxu94]

Add the plugin to the doc https://github.com/apache/skywalking-nodejs#supported-libraries please

[kezhenxu94]

Add the env var to doc please

[tom-pytel]

BTW, I've checked packages request, request-promise and koa and as expected they work by default through the underlying http layer. Should such packages be listed in the docs as "supported" or "compatible" because of this?

[kezhenxu94]

Should such packages be listed in the docs as "supported" or "compatible" because of this?

I think the latter saying makes more sense, let's add a column in the supported libraries table

[tom-pytel]

I think the latter saying makes more sense, let's add a column in the supported libraries table

Go ahead and add the column how you want and when I test packages I will add them there.

[EDIT] Never mind, have a look how I added this.

[kezhenxu94]

@tom-pytel can you please also review #29 , since you're adding 2 plugins for 2 different MySQL libs. Also, if possible, add a test case in this PR?

[tom-pytel]

I can look into adding tests later, right now fighting with a PostgreSQL plugin. If you can merge this before I get the pg plugin done it will make things less messy, especially with the other mysql2 plugin...