feat: add markdown-no-emphasis-keywords lint

[sumitvekariya]

Add markdown-no-emphasis-keywords lint

Summary

Implements a new lint markdown-no-emphasis-keywords that detects uppercase keywords (2+ consecutive uppercase letters) formatted with bold or italic emphasis. This helps maintain consistent formatting standards in EIP documents by preventing inappropriate emphasis on keywords.

Closes #136

What this lint detects ❌

The lint flags uppercase keywords when they are formatted with bold (**text**) or italic (*text*) emphasis:

Bold formatting violations:

**MUST** be implemented          // ❌ Flagged
**SHOULD** follow this          // ❌ Flagged  
**API** documentation           // ❌ Flagged
**HTTP** protocol              // ❌ Flagged
**JSON** format                // ❌ Flagged
**XML** parsing                // ❌ Flagged
**RFC** specification          // ❌ Flagged
**EIP** proposal               // ❌ Flagged

### Italic formatting violations:
*REQUIRED* for compliance       // ❌ Flagged
*OPTIONAL* feature             // ❌ Flagged
*SHALL* implement              // ❌ Flagged
*MAY* include                  // ❌ Flagged
*RECOMMENDED* approach         // ❌ Flagged
*URL* endpoint                 // ❌ Flagged
*SQL* database                 // ❌ Flagged
*CSS* styling                  // ❌ Flagged

[SamWilsn]

Thanks so much for the contribution! I'm sorry it's taken me so long to review. I incorrectly assumed this was spam.