Added CMake option in order to choose encoding type

* Remove extra semicolons
* Fix some int<->uint conversion warnings
* Fix crashing when read_bytes(0)

Make KS_STR_ENCODING_ICONV or KS_STR_ENCODING_NONE mandatory - this has to be an informed decision, not a silent (and hard to debug) workaround

If we don't have zlib => omit declaration from the .h as well as from the .cpp => this way it leads to a clear compile-time error, not link-time error

Link libz and libiconv on Apple platforms

Add build support for macOS, which is missing byteswap.h

We generate different kstruct-derived classes with custom destructors, so kstruct base class destructor must be virtual

Replaced obscure pos_type with solid uint64_t, which are implicity convertible and cause to weird type inferring errors/warnings; should fix clang/MSVC build

correct reading bitfields with sizes between 32bit and 64bit

let type that is left-shiftet to generate a bitmask be of type uint64_t so that bitfields with length 32 to 63 are read properly; add special case for 64 bitfield case; more than 64 bits are not supported at the moment

Return value optimization, according to https://github.com/kaitai-io/kaitai_struct_cpp_stl_runtime/issues/8

kaitai::kstream::reverse for implementing reverse in cpp for strings.

Fix read_bytes() MSVC incompability

Fixed charset conversion error: std::string.resize might reallocate buffer and thus provides no guarantees to keep older pointers valid => we need to re-initialize them