Establish e2e test architecture

[gaocegege]

Ref #10

Signed-off-by: Ce Gao ce.gao@outlook.com

[gaocegege]

I have tried the way in https://forum.processing.org/two/discussion/comment/99658/#Comment_99658

It is interesting :think:

processing$triangle(30, 75, 58, 20, 86, 75)
processing$saveFrame("/private/var/folders/wy/h0plj1mx2398n_dvdtqmxfmc0000gn/T/Processing.R1727552989826233336.tmp.png")
processing$exit()

[gaocegege]

I got the diff factor is 9.4E-4, although I don't what the number means = =

[gaocegege]

But the test will always fail in travis environment:

    [junit] Testcase: test.e2e.core.primitives2d.TriangleTest:test:	Caused an ERROR
    [junit] Forked Java VM exited abnormally. Please note the time in the report does not reflect the time until the VM exit.
    [junit] junit.framework.AssertionFailedError: Forked Java VM exited abnormally. Please note the time in the report does not reflect the time until the VM exit.
    [junit] 	at org.jacoco.ant.CoverageTask.execute(CoverageTask.java:102)
    [junit] 
    [junit] 
    [junit] Running test.e2e.core.primitives2d.TriangleTest
    [junit] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0 sec

We couldn't do this test in CI, it is not cool 🤔

[gaocegege]

Import xvfb to virtualize the framebuffer, now we could run e2e test in Travis CI