html to textfield; multi text objects for more complex text styling

• Merge pull request #178 from singerla/feat-multi-text-helper baf3338
• chore(text): add new functions to readme 282b55d
• chore(text): allow underlined; preserve font style from first paragraph 4416a15
• fix(text): varying styles for text runs 99e5219
• chore(text): allow modification callbacks on pptxGenJS textfields 067504e
• fix(text): apply alignment to paragraph props f1d78f5
• feat(text): use html code for (nested) multi-text content 1e6dfd5
• feat(text): enhance replaceText to support multi-paragraph / multi-textRuns 2d8a587
• chore(slide): add placeholder params to ElementInfo 6c86585

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v0.7.3...v0.7.4