[MS15] Documentation revamp 2/5

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This is the 2^nd of the 5 STF milestones planned to revamp the website and manual.

Deliverable 1: Documentation

• Revamp the F.A.Q. page #2506
• Create a Learn Log4j in under 2 minutes! page #2507
• Create a Concepts page #2508
• Revamp the API page #2535
• Create a Development page #2520
• Revamp the Performance page #2533

Deliverable 2: Log4j Tools 0.9.0

While working on the documentation, we encountered certain issues that required a fix in our infrastructure tooling. We addressed these in Log4j Tools 0.9.0 release. Related tickets from this release are as follows:

Log4j Docgen XSD generator bug

Thanks to our work in MS9 (#1954), we automatically generate an XSD to assist users while configuring their log4j2.xml. Coupled with IDEs' XSD assistance, writing Log4j configuration (i.e., log4j2.xml) has become a breeze. While adding/updating documentation, we explicitly use XSD in every log4j2.xml we share. This not only helps us to validate our own examples, but also enables users to safely copy-paste them, and continue editing with XSD assistance. Though we encountered a small bug in the XSD generator: apache/logging-log4j-tools#117 We fixed this in apache/logging-log4j-tools#120 and re-generated the public XSD.

Add skip parameter to Maven goals

There are several Log4j modules which use the Log4j plugin system. Though some are for testing purposes and should not be reflected in the generated XSD, documentation, etc. That is, Log4j Docgen should discard those modules. To accommodate this need, we added skip configuration knobs to all Maven goals: apache/logging-log4j-tools#121

Support multiple template files

In its current form, the Log4j plugin reference is pretty massive. To experiment with breaking this into multiple pages, we enhanced Log4j Docgen Maven Plugin to support multiple template files: apache/logging-log4j-tools#122