In Python 3.6 a number of escape sequences that were previously accepted
-- for instance "\(" that was translated to "\\(" -- are deprecated. To
retain the previous behavior either raw strings must be used or the
backslash must be properly escaped itself.

Fortran sources with parameters having kind-specifiers
where not correctly intercepted in the crackfortran.py
source.
The reason was a restrictive check for only integer specifiers
which did not split real's into the correct number.

Furthermore, several tests has been added which tests the different
kind specifiers and their use in codes, also all of them together.

Signed-off-by: Nick Papior <nickpapior@gmail.com>

It was committed mistakenly in #7134. `callfortran` is used a lot really.

MAINT: Simplify some tests using temppath context manager.

This replaces code of the pattern

```
fd, name = tempfile.mkstemp(...)
os.close(fd)
try:
   do stuff with name
finally:
    os.remove(name)
```

with

```
with temppath() as name:
    do stuff with name
```

A few more complicated cases are also handled. The remains some
particularly gnarly code the could probably be refactored to use
temppath, but that is a more demanding project.