Add support for controlling the amount of immediate splats

[MikkelBirkeholm]

Before you start, please make sure to:

• Read the doc
• Have tried the latest version
• Search to see if your issue already exists
• Look for / ask questions on Stack Overflow

What problem does this feature solve?

Right now a random amount of splats are created. It would be fairly easy to change the boolean to a number. Use the value as a multiplier.

What does the proposed API look like?

WebGLFluid(document.querySelector('.canvas'), {
    IMMEDIATE: 0 //  Number of immediate splats
    }

[cloydlau]

1. Upgrade to v0.3.4
2. WebGLFluid(document.querySelector('canvas'), { IMMEDIATE: true, SPLAT_COUNT: 3, })