Make sure we are c99

[juniorz]

Why

We want to target our code for the c99 standard.

Tasks

• [x] Remove use of stpcpy
• [x] Remove use of strnlen
• [x] Remove use of getline
• [x] Enable make code-check in the pipeline to avoid this to become a problem again.

[juniorz]

Why not to use gnulib?

https://www.gnu.org/software/gnulib/manual/html_node/Initial-import.html#Initial-import

[claucece]

Check this: https://travis-ci.org/otrv4/libotr-ng/builds/278319205?utm_source=github_status&utm_medium=notification

[olabini]

We should add -std=c99 to all compile commands

[olabini]

We should also add the -pedantic-errors flag so the compiler errors when using non-C99 features.

[claucece]

Thanks! @olabini