cmake: Enable creation of the compile command database by default.

(cherry picked from commit 437a39c7988ae157e2171f57d8c0cfdcc99584f6)
session: Fix a memory leak with custom banner.

BUG: https://red.libssh.org/issues/152
(cherry picked from commit b5efbe75cd7b3881618940f9508b313222176bd8)
channels: Fix exit-signal request.

BUG: https://red.libssh.org/issues/153
(cherry picked from commit 927cd90dc171b7e7a400ab8c1c9474f627e89167)
doc: Improve docs for ssh_channel_get_exit_status().

BUG: https://red.libssh.org/issues/154
(cherry picked from commit adf23533e02d997118d1732f91abf9f116a47cec)
cmake: Install cmake config files to the correct directory.

(cherry picked from commit 291312c5e4774307a79365623065764220a673e9)