Fix typos and improve code quality

[awanawana]

Summary

This PR fixes several typos and bugs in the bash-server.sh script and README.md to improve code quality and portability.

Changes

• Change shebang from /usr/local/bin/bash to /usr/bin/env bash for better portability across different systems
• Fix typo: 'zrite' -> 'write' in comment (line 472)
• Fix typo: 'directoru' -> 'directory' in comment (line 493)
• Fix typo: 'POst' -> 'Post' in comment (line 85)
• Fix typo in README: 'expiremental' -> 'experimental' and 'sendin' -> 'sending' (line 66)
• Fix bug in parseGetData: ${entry#*:} should be ${entry#*=} for URL parameters (line 79)
• Fix bug in parsePostData: ${entry#*:} should be ${entry#*=} for URL-encoded form data (line 90)

Impact

• The bug fixes are important as they affect URL parameter parsing (using : instead of = would break form data parsing)
• The shebang change makes the script more portable across different Unix-like systems
• Typos are cleaned up for better code readability

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