Add a trivial support for UTF-8 encoding
Add a primitive function for reading a byte from input port
Reimplements the function `read_char' for reading any utf-8 character
Delete some unnecessary comments in file `proc.c'
Do in file `object.c' as in file
Reimplements the C code for library function `string-ref'

Now the C function `string_ref' is able to process the UTF-8
character, although it cost O(n) time complexity.
Add a trivial support for constructing a string contains UTF-8 characters
Fix a bug in function `init_wchar'

The original length computation is wrong and cause too much copying of
characters from parameter `bytes' --- The `init_wchar' should assume
its argument to be an array of bytes, and these bytes makes a complete
UTF-8 encoding of an character.
Improves the function `string_ref' for supporting UTF-8 character
Add the support for UTF-8 characters in `string-length'
Implements the function `string_set' for WSTRING
Supplements the process for STRING in function `string_set'
UTF-8 is done!
Merge branch 'feature-utf-8' into develop