Update tokens-and-mail-merge.md on Line 142 eg should always be "E.G." same is...

Update tokens-and-mail-merge.md on Line 142 eg should always be "E.G." same is "I.E." I also removed the line break after the second E.G. to clean up the code slightly.

In Lines 255, 297, 304, and 311 added . period after "Footer".

In Lines 262, 269, 276, 283, 290, 318, and 325 added . period after Resubscribe. Also capitalized "UNSUBSCRIBE and RESUBSCRIBE" and added spaces after , commas.

In Lines 332 and 339 added a . period after "elsewhere".

In Lines 346, 353, 360, and 367 added . period after "templates".

In Lines 374 and 381 added . period after "Optout". Also capitalized "RESUBSCRIBE, UNSUBSCRIBE, and OPTOUT" and added spaces after , commas.

In Line 388 added . period after "Body".

In Line 395, 409, and 416 added . period after "Message". "Message" in 416 was capitalized.

In Line 402 added . period after "request".

These changes were made for consistency in the document and proper grammar rules.