factor out cdef definitions into operator.pxd

This allows subclassing of operators by third party libraries
(e.g. tkwant).
19 jobs for v1.4.0rc0 in 39 minutes and 39 seconds (queued for 2 seconds)
latest
Status Name Job ID Coverage
  Build Env
manual build-env:conda #51641
allowed to fail manual
manual build-env:debian #51640
allowed to fail manual
manual build-env:default #51642
allowed to fail manual
manual build-env:ubuntu #51639
allowed to fail manual
 
  Build
passed build:debian #51644

00:02:30

passed build:latest #51647

00:02:09

passed build:no-extras #51646

00:02:05

passed build:stable #51645

00:02:07

passed build:ubuntu #51643

00:02:15

 
  Test
passed build PDF documentation #51656

00:04:54

passed build documentation #51655

00:04:51

failed check for broken links in doc #51657
allowed to fail

00:01:24

passed check for dependencies installed #51649

00:00:25

passed check whitespace style #51648

00:00:29

passed test:debian #51653

00:34:25

passed test:latest #51654

00:36:57

passed test:no-extras #51651

00:37:07

passed test:stable #51650

00:37:08

passed test:ubuntu #51652

00:35:10

 
Name Stage Failure
failed
check for broken links in doc Test
(line   39) ok        http://www.numpy.org/
writing output... [100%] tutorial/superconductors


build finished with problems, 156 warnings.
make: *** [linkcheck] Error 1
Makefile:119: recipe for target 'linkcheck' failed
make: Leaving directory '/builds/kwant/kwant/doc'
ERROR: Job failed: exit code 1