Made examples and demo optional build options in cmake

[SleepProgger]

I added following build options to make building as subproject a bit more comfortable.

• agg_BUILD_EXAMPLES
• agg_BUILD_DEMO
• agg_BUILD_PLATFORM
• agg_BUILD_CONTROLS

agg_BUILD_PLATFORM and agg_BUILD_CONTROLS are forced to true if either agg_BUILD_EXAMPLES or agg_BUILD_DEMO are set.
So by default nothing should have changed as examples and the demo are defaulting to ON.

Not sure this is of interest for you, but it can't harm to try to get it "upstream".

[ghaerr]

Hello @SleepProgger,

Thanks for the PR! I've been a bit buried in other work but hope to be able to review this and get it committed soon. I myself haven't used CMake on this project, but your changes look useful for those who do.

Not sure this is of interest for you, but it can't harm to try to get it "upstream".

I'll reach out... there have been few changes on Sourceforge in the last couple years, almost all small changes, nothing functional. I have been thinking of updating this repo with those changes as well.

Thank you!