write specification for eda_text_columns function along with dependencies

[charlessuresh]

Did the following:

• wrote function documentation / specifications for eda_text_columns function
• set-up empty functions (with appropriate function names) containing no code
• added import statements needed for eda_text_columns function

@adibns is my dedicated reviewer for this week. @lephanthuymai @rahulkuriyedath please feel free to suggest / review / comment

[adibns]

It is good