- Replace strdup(s) with cfg_strdup(funname, s) that exits on out of mem
- Replace malloc(n) with cfg_malloc(funname, n) that exits on out of mem
- Change multiline string scanning in lexer.l to avoid core dump
- Remove global variables string_buf and string_bug_ptr
- Ensure reading strings unescapes strings C-Style
- Ensure writing strings escapes strings C-Style again
Commit looks longer than needed as unescape() and auxiliary functions needed
to be moved from term.c (not in libavrdude) to config.c (in libavrdude).