Adds support for configuring FILENAME with %fbase.

[xinwf]

1.Set level output with a fixed width 2.Allowing user configure fbase in log filename with conf file

This is a

• Breaking change
• New feature
• Bugfix

I have

• Merged in the latest upstream changes
• Updated CHANGELOG.md
• Updated README.md
• Run the tests

Example of this feature:

* GLOBAL:
    ENABLED                 =   true
    TO_FILE                 =   true
    TO_STANDARD_OUTPUT      =   true
    FORMAT                  =   "%datetime{%H:%m:%s} %level %fbase:%line] %msg"
    FILENAME                =   "/tmp/LOG/%datetime{%Y%M%d}/%fbase.log"
    MILLISECONDS_WIDTH      =   3
    PERFORMANCE_TRACKING    =   false
    MAX_LOG_FILE_SIZE       =   1048576
    LOG_FLUSH_THRESHOLD     =   0
	
* VERBOSE:
    ENABLED                 =   false

I have test with CMakeLists with g++14.