Fix output filenames that contain a forward slash or backslash

[MJacred]

Example table

CREATE TABLE IF NOT EXISTS `Slash/Test` (
    id INT UNSIGNED NOT NULL AUTO_INCREMENT,

    `my_en/um` ENUM('test/1', '/test2', 'test3'),

    PRIMARY KEY (id)
);

Sqlboiler attempts to create a file called "Slash/Test.go", which it fails to do - and should not do. This fix changes the output to "Slash_Test.go".

NOTE: this output also requires volatiletech/strmangle#17 and volatiletech/strmangle#18

// SlashTest is an object representing the database table.
type SlashTest struct {
	ID     uint                `csv:"id" hash:"id" boil:"id" json:"id" toml:"id" yaml:"id"`
	MyEnUm SlashTestNullMyEnUm `csv:"my_en/um" hash:"my_en/um" boil:"my_en/um" json:"my_en/um,omitempty" toml:"my_en/um" yaml:"my_en/um,omitempty"`

	R *slashTestR `csv:"-" hash:"-" boil:"-" json:"-" toml:"-" yaml:"-"`
	L slashTestL  `csv:"-" hash:"-" boil:"-" json:"-" toml:"-" yaml:"-"`
}

// and in boil_types.go

type SlashTestMyEnUm string

// Enum values for SlashTestMyEnUm
const (
	SlashTestMyEnUmTest1 SlashTestMyEnUm = "test/1"
	SlashTestMyEnUmTest2 SlashTestMyEnUm = "/test2"
	SlashTestMyEnUmTest3 SlashTestMyEnUm = "test3"
)

[MJacred]

@stephenafamo: This PR together with volatiletech/strmangle#18 would add support for table names containing slashes