Group SVG elements and add “id”, “class” and formatting options

[cecilios]

This PR does the following changes:

• Adds wrapper <g> elements when required, for grouping all the SVG elements generated by a music notation (e.g. a note).
• When option enabled, adds attributes id and class to all SVG elements, as required, so that the user application can identify and manage the generated SVG code.
• Adds formatting options for SVG output (new lines, indentation) to facilitate reading by humans.

For instance, now it is possible to generate something as:

<g id='m83' class='note'>
    <path class='ledger-line' ... />
    <text class='notehead' ... >...</text>
    <path class='stem' ... />
</g>

For detailed information, see the new added file docs/api/mainpages/render-svg.h in this PR. This file contains the documentation for updating the public API documentation when this PR is merged.

Other non-related changes

• Added script to regenerate and upload API documentation.
• When only using SVG, Lomse initialization is no longer required. SVG sample code has been updated.