Correct/update information about available serial ports for each board

[per1234]

The Serial reference pages contained large amounts of incorrect or extremely outdated information about which serial ports were available for each board.

• Add a table to the Serial reference homepage which lists the available ports for each board. Previously, this was done in a verbose manner that does not lend itself to the ever increasing information that must be conveyed on this topic as new boards are added.
• Rather than document syntax for each of the list of possible serial objects, only document each function signature and then point the reader to the list of available ports for each board in the homepage.
• Fix miscellaneous incorrect or outdated information about ports throughout the Serial reference pages.

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I'm not perfectly happy with putting the Serial object documentation under the "Parameters" section, since it's not really a parameter, but this follows the convention established in several other reference pages:

• reference-en/Language/Functions/Communication/Stream/streamAvailable.adoc

  Line 29 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamFind.adoc

  Line 30 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamFlush.adoc

  Line 30 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamParseFloat.adoc

  Line 30 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamParseInt.adoc

  Line 37 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamPeek.adoc

  Line 30 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamRead.adoc

  Line 30 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamReadBytes.adoc

  Line 32 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamReadBytesUntil.adoc

  Line 32 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• reference-en/Language/Functions/Communication/Stream/streamSetTimeout.adoc

  Line 28 in b0791f1

  `stream` : an instance of a class that inherits from Stream.

• -https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/charat/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/compareto/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/endswith/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/equals/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/equalsignorecase/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/getbytes/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/indexof/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/length/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/replace/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/setcharat/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/startswith/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/substring/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/tochararray/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/toint/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/tofloat/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/tolowercase/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/touppercase/
• https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/trim/
• https://www.arduino.cc/en/Reference/ServoAttach
• https://www.arduino.cc/en/Reference/ServoWrite
• https://www.arduino.cc/en/Reference/ServoWriteMicroseconds
• https://www.arduino.cc/en/Reference/ServoRead
• https://www.arduino.cc/en/Reference/ServoAttached
• https://www.arduino.cc/en/Reference/ServoDetach

I welcome any proposals for better ways to do that.

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Reference: http://forum.arduino.cc/index.php?topic=489217.msg3341839#msg3341839