Add locale for en-IN

[lauft]

The following locale needs to be verified/completed:

class en_IN(Locale):
    """
    01-01: [NF] New Year's Day
    12-25: [NF] Christmas
    : [NV] Lohri
    : [NV] Pongal, Makar Sankranti
    : [NV] Guru Gobind Singh Jayanti
    : [NV] Republic Day
    : [NV] Vasant Panchami
    : [NV] Guru Ravidas Jayanti
    : [NV] Maha Shivaratri
    : [NV] Chhoti Holi, Holika Dahan
    : [NV] Holi
    2 days before Easter: [NV] Good Friday
    Easter: [NV] Easter
    : [NV] Gudi Padwa, Ugadi
    : [NV] Solar New Year, Baisakhi
    : [NV] Rama Navami
    : [NV] Hazarat Ali's Birthday
    : [NV] Buddha Purnima
    : [NV] Eid al-Fitr , Ramadan
    : [NV] Independence Day
    : [NV] Rakhi, Raksha Bandhan
    : [NV] Krishna Janmashtami
    : [NV] Ganesh Chaturthi
    : [NV] Onam, Eid al-Adha, Bakrid
    : [NV] Gandhi Jayanti
    : [NV] Durga Ashtami
    : [NV] Maha Navami
    : [NV] Dussehra, Madhvacharya Jayanti
    : [NV] Muharram
    : [NV] Valmiki Jayanti
    : [NV] Karwa Chauth
    : [NV] Diwali, Lakshmi Puja
    : [NV] Gowardhan Puja
    : [NV] Bhaiya Dooj
    : [NV] Chhath Puja
    : [NV] Guru Nanak Jayanti, Nehru Jayanti
    : [NV] Milad an-Nabi, Id-e-Milad
    """

    locale = "en-IN"
    easter_type = EASTER_WESTERN

Checklist:

• Are all holidays (i.e. days "which are defined by law on which business or work are suspended or reduced") listed? Can you provide the legal sources which define the holidays?
• Is the spelling correct?
• Are the fixed dates <month>-<day> correct?
• If a holiday has a variable date: Is the algorithm to calculate it correct/can you provide it if missing? If it depends on the easter date: Is it the western or orthodox easter date?
• If a holiday is proclaimed by the government: Can you provide the source?
• Are holidays moved to a different date, e.g. if they fall on a saturday/sunday/...?
• Are holidays observed on a different date (is there a substitute holiday), e.g. if they fall on a saturday/sunday/...?
• Are the flags correct? (N = national holiday, defined by law, R = holiday with religious background, F = holiday with fixed date, V = holiday with variable date)
• Have there been any holidays renamed/deleted/created since 2011? If yes, which ones and since when?