Add code generator for convolutional codes

Add python utility to generate .c code with convolutional
encoder/decoder based on polynomial description of the code. If argument
given it'll be interpreted as intended output directory, otherwise
current working directory is used.

Codes for *CCH, CS2/3 and TCH/AFS are generated. Corresponding manual
implementations are removed from tests. This introduce build-time
dependency on python.

The main work for this patch was generously contributed by Sylvain
Munaut.

Fixes: OS#1629
diff --git a/debian/control b/debian/control
index 459030b..42ebdba 100644
--- a/debian/control
+++ b/debian/control
@@ -39,6 +39,7 @@
 Package: libosmogsm5
 Section: libs
 Architecture: any
+Build-Depends: python (>= 2.7.6)
 Depends: ${shlibs:Depends}, ${misc:Depends}
 Multi-Arch: same
 Description: Osmo GSM utility library