* Create telemetry_mssql.sql
SQL to create the speedtest_users table on Microsoft SQL server.
This SQL is based on the original templates, and continues to uses nvarchar for all fields as the templates do – even though some of the fields should be int.
* Added support for Microsoft SQL Server
* New sanitycheck.php page plus required updates to telemetry_db.php
Created a sanity check page to verify that the required PHP extensions are installed, and that it is possible to connect to the database.
* Update README.md - MS SQL support
Added mention of Microsoft SQL Server as a supported DB engine.
* Added missing <tr> to sanitycheck.php
* put code to insert and query data from database into separate file
* simplify obfuscation salt file handling
* use new DB interaction functions in telemetry.php
* use new DB interaction functions in stats.php
and fix indentation levels
* format telemetry settings file
* use new function for interacting with DB in index.php
* move drawing of the image into function and try to comment each section with what it does
* reorder lines for parts of the image to align with the order they appear on the image
* bugfix: display obfuscated and deobfuscated id in stats if id obfuscation is enabled
* improve error handling
* add missing PHPDocs to functions
* imageftbbox returns an array on success and false on failure so to check if the font is usable, check if we got an array
* fix dsn for postgres
* fix limit sql statement for postgresql
* remove obsolete require statement
* use require instead of require_once since the settings file might need to be loaded multiple times
because it just contains plain variables which will just get loaded into the current scope
* move require statements to the top of the file
* make sure files are readable before requiring them
* add constant to refer to the telemetry settings file and check if it is readable before loading it
* return null if no speedtest result was found for the given id and show according message to the user instead of just exiting
* use existing constant instead of string for telemetry settings file name
* uniformly use single quotes instead of double quotes as most code places already used single quotes
* somehow some tabs sneaked in, replace them to uniformly use spaces
* mysql now uses pdo, too, reflect that in the requirements documentation
* pass username and password as constructor parameters instead of via DSN
