Add generation of documentation using doxygen

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Fix libkeymap.pc installation

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Rename *_exist to *_exists

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Add getter and setter for parser flags

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Move lk_ctx content to private part of library

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>