Multiline string support (#156)

* refactor dotenv parser in order to support multi-line variable values declaration

Signed-off-by: x1unix <denis0051@gmail.com>

* Add multi-line var values test case and update comment test

Signed-off-by: x1unix <denis0051@gmail.com>

* Expand fixture tests to include multiline strings

* Update go versions to test against

* Switch to GOINSECURE for power8 CI task

* When tests fail, show source version of string (inc special chars)

* Update parser.go

Co-authored-by: Austin Sasko <austintyler0239@yahoo.com>

* Fix up bad merge

* Add a full fixture for comments for extra piece of mind

* Fix up some lint/staticcheck recommendations

* Test against go 1.19 too

Signed-off-by: x1unix <denis0051@gmail.com>
Co-authored-by: x1unix <denis0051@gmail.com>
Co-authored-by: Austin Sasko <austintyler0239@yahoo.com>

README.md

@@ -75,8 +75,8 @@ import _ "github.com/joho/godotenv/autoload"
 While `.env` in the project root is the default, you don't have to be constrained, both examples below are 100% legit
 
 ```go
-_ = godotenv.Load("somerandomfile")
+godotenv.Load("somerandomfile")
-_ = godotenv.Load("filenumberone.env", "filenumbertwo.env")
+godotenv.Load("filenumberone.env", "filenumbertwo.env")
 ```
 
 If you want to be really fancy with your env file you can do comments and exports (below is a valid env file)

fixtures/equals.env

@@ -1,2 +1 @@
 export OPTION_A='postgres://localhost:5432/database?sslmode=disable'
-