Add comprehensive libipcon API documentation

[saimizi]

Summary

• Added comprehensive libipcon API documentation as Document/libipcon-api.md
• Complete reference for all 16 API functions with clear examples
• Table-based format for better readability and navigation
• Includes data structures, constants, and complete usage examples

Features

• Table of Contents for easy navigation
• Structured Tables for each function with signature, description, parameters, and return values
• Usage Examples as separate subsections with proper C code formatting
• Complete Example showing basic application flow
• Data Structures documentation for all message types and callback structures

Test plan

• Document is properly formatted in markdown
• All API functions from lib/libipcon.h are documented
• Usage examples compile and follow library patterns
• Table of contents links work correctly

🤖 Generated with Claude Code

[saimizi]

Coverage Summary

Summary coverage rate:
  lines......: 21.8% (186 of 854 lines)
  functions..: 21.7% (13 of 60 functions)
  branches...: 15.1% (77 of 511 branches)

Coverage Detail

Filename                   |Rate     Num|Rate    Num|Rate     Num
=================================================================
[/home/runner/work/libipcon/libipcon/]
driver/ipcon.h             |    -      0|    -     0|    -      0
lib/libipcon.c             |69.6%     56|8500%     4|    -      0
lib/libipcon_dbg.c         |16.7%      6|1000%     1|    -      0
lib/libipcon_priv.c        | 9.5%    116|1614%     7|    -      0
lib/libipcon_priv.h        |50.0%      2|    -     0|    -      0
lib/util.c                 | 117%      6|2400%     1|    -      0
=================================================================
                     Total:|32.3%    186|3931%    13|    -      0