(cherry picked from commit c5a6cae8)

* Renames `sender` to `source`.

The naming variable was incorrect.  The source of the funds is *not* necessarily (and in most cases isn't) the sender of the transaction.  Also, this code has a `msgSender` which further adds confusion.

* Changes to `from/to` instead of `source`.

* Function documentation matches new names

* Changed other instances of sender/recipient to from/to.

Also changed `msgSender` to `owner` in the approval related methods.

* apply changes to IERC20.sol + minor renaming in ERC20.sol

Co-authored-by: Daniel Von Fange <daniel@leancoder.com>
Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
(cherry picked from commit 63b46690)

(cherry picked from commit ec097571)

(cherry picked from commit cefe6bde)

Remove repeated word "the".

(cherry picked from commit ae54e6de)
Signed-off-by: Hadrien Croubois <hadrien.croubois@gmail.com>

* Make royaltyInfo(uint256 _tokenId, uint256 _salePrice) virtual

Should be cherrypicked in release 4.5

* fix lint

(cherry picked from commit 6fb1e843)
Signed-off-by: Hadrien Croubois <hadrien.croubois@gmail.com>

Co-authored-by: Han Lin Yap <codler@users.noreply.github.com>
(cherry picked from commit 25eeb80b)
Signed-off-by: Hadrien Croubois <hadrien.croubois@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
(cherry picked from commit 3eb2d43b)
Signed-off-by: Hadrien Croubois <hadrien.croubois@gmail.com>

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
(cherry picked from commit 85566fae)

(cherry picked from commit bfd05d96)

(cherry picked from commit fc01c51c)

(cherry picked from commit f55d2716)

(cherry picked from commit d57593c1)

(cherry picked from commit 7c47ac71)

(cherry picked from commit 3da61964b9bf6c4f150b8fe7bc8532f3a2973374)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* add contract and tests

* avoid implicit cast

* add test cases

* fix test names

* modify avarage and add tests

* improve signed average formula

* fix lint

* better average formula

* refactor signed average testing

* add doc and changelog entry

* Update contracts/utils/math/SignedMath.sol

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* remove ceilDiv

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* add feature request #3084

* Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* Add changelog note

* add documentation

* test unlimitted allowance and add ERC777 unlimitted allowance

* reference PR in changelog

* documentation IERC20 -> ERC20

* use asciidoc note syntax

* use asciidoc note syntax

* typo

* typos

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* Name missing return variable in IERC721Enumerable

For consistency among all functions.

* remove return variable names