Add const to member functions in StringUtil and its derived classes

In particular, explicitly adding const to StringUtil::showString would be
important because it could be used a lot by clients when they want to get
a std::string object from the internal representation of KyTea's string.

Also, add comments regarding the thread safety to mapChar and mapString.
Use Travis CI to build and test KyTea

- Change README to markdown to display the build status in Travis CI
- Add the build status of Travis CI
- Fix the automake error due to missing README
Enable running unit tests with make check.

This is also useful to automate the process of building and testing.
Initialize Kytea object better way

- Initialize member variables in the initializer list instead of initializing
  in the body of the constructor.
- Reorder the private members to follow the initialization order,
  which is described in paragraph 5 in 12.6.2 in C++98 spec.  For the record,
  the basic rule is that the members will be initialized in the order they
  are declared.
- Use explicit for the constructor
Make Kytea object non-copyable explicitly

It would be better to emit errors in compile time as soon as users try to copy
the object in their C++ programs, instead of getting SIGSEGV when users run
the programs which use copied objects inside of them.  For the users who want to
use Kytea objects without knowing the details, that runtime errors sound weird,
and possibly hard to debug.
Change GitHub URL and branch to display the status of Travis CI
Reformat with clang-format
Add the project name the #define guards in every header

Terminate namespaces with comments.
Fix C++11 -Wnarrowing
Delete unused headers
Use const instead of define macros.
Use enum

Refactor corpus format type
Delete unnecessary forward declaration.
Delete no-effect const
Fix -Wundef warnings

Use `#ifdef` or `defined` instead of `#if`.
Fix -Wweak-vtables warnings.

See the details at http://www.chromium.org/developers/coding-style/chromium-style-checker-errors#TOC-Virtual-Method-Out-of-lining,
for example.
Fix more -Wignored-qualifiers warnings
Delete extra semicolons [-Wextra-semi].
Fix the use of the C++11 extension for enum
Add a script to find memory errors using ASan

Set up memory error check in Travis CI.