core: rewrited to don't use getcontext/swapcontext due to *context functions works buggy on some combinations of kernel/gcc/glibc

cli: fixed cpu/mem utilization statistics

radius: fixed bug of double packet free when second DM request received in time when radius sends Accounting-Request Stop

ppp: fixed memory leak when ipcp raises error at ConfReq

log: simplified engine
various bug fixes

        and newly introduced -  ip-change, when radius CoA request received,
        also this module manages pppd compatible radattr.pppX files
core:   implemented module 'sigchld' which handles SIGCHLD signal,
        waits child processes to terminate and manages pid terminate handlers

log: implemented log_file logging target with per-user/per-session support

radius: implemented PAP authorization
radius: implemented IP assigning
triton: implemented userspace context switching
and other stuff