spelling error in codegen.rst
spelling fix in codegen.py
Changed method finding func

The earlier method of finding func was incomplete. This new method is more robust and less likely to fail. This method is still in progress.
func modification to solve nonlinear sysode of 2 eq order1 type5

Earlier there was error comming in solving the type 5 of nonlinear sysode of 2 equations due to problem in function returned which was `[y(t), y(t)]`. This commit contain modification such as to remove that error. This also places the @XFAILed test back to normal.
Replaced `func` with `funcs` and vice versa

At some places func was used for many functions and funcs was used for single function. This commit replaces that in classify_sysode
Corrected comment
typo fix in codegen test
modify 4 minute test so it takes about 2 seconds

Before original commit:
>>> series(cot(x**4 + x**5), x, 0, 1)
O(x)

After original commit
>>> series(cot(x**4 + x**5), x, 0, 1)
x**(-4) - 1/x**3 + x**(-2) - 1/x + O(x)

This simpler test failed in master before the original
changes but succeeds afterwards demonstrating that the
change worked. It also takes orders of magnitude less time
to compute.

Since the time that the correction was made, another correction
was made that includes the "+1" term; that is now included in the
modified test, too.
longer underline
Add function to calculate transmitted vector after refraction [skip ci]
Change the name of function to refraction_angle and fix a typo [skip ci]
Make refraction_angle compatible with Ray3D and plane. [skip ci]
Add test_util
Add deviation [skip ci]
Fix a bug in deviation while using plane. [skip ci]
Add tests for refraction_angle and deviation
Remove unused imports
UnXFAIL a failing test
Merge pull request #7751 from smichr/slow

modify test that took 4 minutes to compute
Merge pull request #7768 from cbm755/typofix

Minor typo fixes in docs