A value is recognized as CONFIG_TYPE_INT if it's only numbers, and
CONFIG_TYPE_INT64 if it's numbers followed by L or LL. However from a
user point of view adding L or LL is confusing. Instead, if the
integer is too big to fit in an int, return a CONFIG_TYPE_INT64. This
also avoid silent truncation.

Add the existing tests and the examples. The testsuite is then run with
"make check".

Do not display compilation command lines, unless make is called with
V=1.

(which were infinitely recursive).

Made all exception constructors public.

- added Setting.lookup() and config_setting_lookup()
- documentation updates
- version bump

it's allow to generate libconfig exception in user code
example:
libconfig::Setting& obj = ...;
if ( !obj.isGroup() )
    throw libconfig::SettingTypeException( obj, "TypeGroup expected" );

To address hyperrealm/libconfig#3, I have added a SettingIterator class
and begin() and end() methods on Setting so that lists and arrays of
Setting can be iterated through using C++ style iterators.

There is an iterator as well as const_iterator defined for the class.

To address hyperrealm/libconfig#4, `Config::operator[](const char*)` and
`Setting::lookup(const std::string& key)` have been added.

Note: `operator[]` had to remain as `const char*` to avoid ambiguities
      in some situations.

To address hyperrealm/libconfig#1, the cast operator from Setting to
const char* has been removed. As a result, lookupValue() taking a const
char* has also been removed as it uses the cast operator.

This change allows code that assigns directly to a std::string or a
const char* to compile without errors. No change to existing code should
be required.

To address hyperrealm/libconfig#2, a constructor has been added to the
header and source file.