Move macro.h to shared directory

It's not really related to libkmod, so move it to a directory in which
we keep common stuff.
Move missing.h to shared directory
Move generic util functions to shared directory
build-sys: normalize line breaks

Break lines earlier, as it's already done in some places and use only 1
tab to avoid reaching the column limit.
Move array implementation to shared directory
Move hash implementation to shared directory
Reorder and reorganize header files

Let the includes in the following order:

< system headers >
< libkmod >
< tool >
< local headers >
Prefer inttypes.h over stdint.h
Rename getline_wrapped() to freadline_wrapped()
Clarify what licences apply where

This doesn't change any license, just clarifies what's licensed under
LGPL and what's under GPL.
testsuite: add tests for array implementation
Do not export array of kmod extensions

The only user outside of libkmod-util is depmod, which really only needs
to get the string for the extension of uncompressed modules. It doesn't
need to access the array itself.
Do not rely on prio_to_str() being always inline

This function was declared as always-inline so there was not really a
problem in returning prioname, that could possibly point to the local
buf[] variable.

However static analysis tools are often confused about this and being
always-inline was just a workaround to make it work.

So, let's move the buffer to the caller. We have only 2 callers so it
doesn't matter much. This always reduce the size of log.o, since now the
function is not inlined anymore. Below is the size for "-g -O2" with
gcc:

before:
   text    data     bss     dec     hex filename
   1325       4       1    1330     532 tools/log.o

after:
   text    data     bss     dec     hex filename
   1171       4       1    1176     498 tools/log.o
Move alias_normalize() to shared
depmod: use alias_normalize() from shared

Remove underscores2() function which is essentially the same as
alias_normalize() and the latter, which is now in shared/.
Move remaining functions from libkmod-util to shared
build-sys: rename libkmod-util convenience library

Now that all source code from libkmod-util has been moved to shared/
directory, rename also the convenience library to libshared.
Log error on failed underscores(), moving it to shared/

Move underscores() to shared/. It's the same as alias_normalize(), but
it rather operates in place, with the same string being passed.

The difference now that it's in shared/ is that it's a non-logging
function.

This makes us a little bit more verbose: we don't accept partially
correct module and aliases names in kcmdline and in configuration files.
We log an error instead.
Change parameter from int to char

It's a char not an int.
libkmod: remove unused inline functions

libkmod/libkmod-list.c:39:33: warning: unused function 'list_node_next' [-Wunused-function]
static inline struct list_node *list_node_next(const struct list_node *node)
                                ^
libkmod/libkmod-list.c:47:33: warning: unused function 'list_node_prev' [-Wunused-function]
static inline struct list_node *list_node_prev(const struct list_node *node)
                                ^

It doesn't really matter in the end result since the compiler won't
generate any code for it. But let's keep it clean. It wasn't needed
until now, so probably it won't be anymore.