build system (v0), add long options

• mojitos now supports long options, via "optparse.h", written by wellons@nullprogram.com and released into the public domain
• one can choose which captor to include or exclude in the final binary with configure.sh.
• makefile is now POSIX compliant (or at least, should be).
• one now have to fill in the "struct optparse_long" and "struct captor" structs when adding a new captor.
• defined a hard limit to the numbers of fixed options (10), and to the amount of captors (20). These can be changed by modifying NB_MAX_OPTS and NB_MAX_CAPTORS, respectively.
• mojitos now includes "captors.h", generated by the configure.sh script
• changed the signature of add_source() to: void add_source(struct captor*, char*)
• main() now must call the init_captors() function.